Versioned Sources and Frozen Citations in a Medical Learning RAG
Our source lifecycle separated active retrieval from saved citation snapshots, preserving history after replacement while deleted files could return 404
Technically reviewed by Dmytro Nasyrov on .
A source update should change what a new question can retrieve. It should not silently rewrite the references attached to yesterday's answer. We needed both behaviors in the learning platform we were building for aesthetic medicine, and one mutable document record could not express them clearly.
Our September source-management design separated the document, its uploaded versions and the version currently eligible for search. Later, the conversation-history design stored a citation snapshot with each answer. The two decisions solved different parts of the same problem: current retrieval needed controlled change, while historical explanations needed stable identity.
Latest upload and active source were different facts
Uploading a replacement did not immediately remove the working source. The new version entered PENDING beside the existing active version. Parsing and indexing could then succeed or fail without requiring the newly uploaded file to be treated as already searchable.
After successful indexing, the new version became active and the previous version became superseded. A failed upload remained a failed version. The design also allowed an indexed or superseded version to be activated deliberately, which provided a rollback path without uploading the old file again.
That distinction affected the administration contract. The document's displayed status could reflect the latest version, including work still in progress. A separate activeVersion identified the source used by retrieval. An operator seeing a processing upload therefore needed both facts, rather than one ambiguous status label.
Search eligibility lived on the fragments
The vector store retained points for source versions and carried the version identifier and lifecycle status in each point's payload. Retrieval filtered for active points. Superseding a version changed its eligibility; it did not require generating its embeddings again merely to preserve the version for possible rollback.
| Operation | Effect on new retrieval | Historical answer boundary |
|---|---|---|
| Upload a replacement | Existing active version remains available while the upload processes | Earlier citation snapshots remain unchanged |
| Activate a version | Selected indexed version becomes eligible; the former active version is superseded | Saved answers keep their original version identity |
| Retire a document | Its fragments leave the active search scope | Retirement does not rewrite saved citations |
| Delete source files and versions | Associated source data and vector points are removed | Snapshot text survives, but its file link can return 404 |
Updating source metadata propagated payload changes across the document's versions. Search eligibility and document identity were therefore explicit data, rather than a convention hidden in a filename. The design's hard active-status filter also preceded ranking preferences: a favored document was still ineligible while retired or superseded.
A replacement was safer than rebuilding the active version
Our indexing notes described deterministic point identifiers built from the version and chunk index. Reindexing first removed that version's old points, then wrote the rebuilt set. This prevented leftover chunks from surviving when a revised extraction produced fewer fragments.
It also exposed a tradeoff. Reindexing the same active version could temporarily remove its searchable fragments. Uploading a new version beside the active one had a different lifecycle. Treating these operations as equivalent would hide an availability gap from the administrator.
This was a documented implementation boundary, not a claim of an atomic transaction spanning relational storage and the vector database. The lifecycle made the intended states inspectable. It did not eliminate every interval in which stores could be out of step.
The answer stored its citation, not a live join
The September 30 history design made a citation a snapshot attached to a saved answer. It stored the reference fields, including the version identifier and label, rather than depending on a foreign key to a fragment that could later disappear. Replacing a source would consequently affect future retrieval without changing what an older answer said it had cited.
There was a deliberate limit: deleting the underlying version file could make the stored file URL return 404. The snapshot preserved an explanation of the reference, not guaranteed permanent access to the original bytes. A product requiring immutable source access would need an additional retention policy and storage commitment.
The distinction matters when an older answer looks inconsistent with the current library. The first question is which version it used. Replacing the old reference with today's active source would make the interface look tidy while destroying that explanation.
Checks at the boundary between present and past
A useful lifecycle check follows one saved answer through replacement, rollback and retirement. Its citation identity should remain the same while a new query uses the currently active version. Deletion adds a separate check: the answer must remain readable even if opening its source file fails. Those are engineering checks implied by the design, not clinical validation.
The records also caution against inferring answer quality from a lifecycle test. Removing a preferred source does not prove the generator will refuse: another active fragment may still pass retrieval. Eligibility, ranking and support for a particular claim require separate inspection.
Our article on saving streaming answers through Stop and Retry covers when an answer becomes durable. Source versioning answers a later question: after it is durable, which changes may affect its references? In this design, future searches follow the active version and saved answers keep the citation they received.
Evidence scope: the September 23 document-administration specification, its September 24 implementation clarifications and the September 30 chat-history specification. This account describes recorded lifecycle and persistence decisions, including the accepted broken-file-link boundary.
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How long have you been in business?
Pharos Production has been in business since 2013, with over 13 years of experience in custom software development. During this time, we have delivered over 110 applications for 200+ clients across 28 industries, including FinTech, healthcare, crypto and e-commerce. We are rated 5/5 on Clutch based on 107 verified reviews (2026).
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What services do you provide?
Pharos Production provides six core service categories: AI Development (LLM applications, AI agents, machine learning and computer vision), Blockchain and Web3 (smart contracts, DeFi, tokenization on Ethereum, Solana, TON and other chains), FinTech Development (payment platforms, digital banking, KYC and AML integration), Software Development (mobile apps, web platforms, database design, UI/UX), Security and QA (code audits, penetration testing, smart contract audits, manual and automated testing) and Consulting (architecture design, MVP validation, startup consulting).
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Where is Pharos Production located?
Pharos Production is headquartered in Las Vegas, Nevada, USA (5348 Vegas Dr, Las Vegas, NV 89108), with an engineering office in Kyiv, Ukraine (44-B Eugene Konovalets Str. Suite 201, Kyiv 01133). We work with clients worldwide and provide remote collaboration across all time zones. Visit our contact page for directions and scheduling options.
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How big is your team?
Pharos Production has a team of 90+ engineers, including software developers, blockchain specialists, QA engineers, DevOps experts, UI/UX designers, project managers and solution architects. Our founder, Dr. Dmytro Nasyrov, holds a PhD in Artificial Intelligence and leads the technical direction of all projects.
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What types of customers do you serve?
We serve a wide range of clients, from startups and product companies to mid-sized enterprises and large institutions. Our clients include crypto exchanges, FinTech providers (like Pleenk), healthcare organizations, sportsbook operators (like Pro Gambling), e-commerce platforms and SaaS companies. Pharos Production has worked with 200+ clients across 28 industries since 2013, adapting engagement models to match each client's stage, whether it is MVP validation for a startup or enterprise-scale development for an established business.
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How is a custom software development company different from an agency?
A custom software development company like Pharos Production assigns one dedicated engineering team that owns your product across multiple release cycles, instead of handing it off once a contract ends. Agencies more often rotate staff between clients and optimize for fast delivery over long-term product ownership.
Pharos Production keeps the same team on your codebase through 2-week sprints, so there is no re-onboarding cost each time you request a new feature.
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How much does custom software development cost?
Custom software development costs vary based on project scope and complexity. At Pharos Production, typical project ranges are: MVP development ($10,000-$25,000), suitable for startups validating a product idea; full-fledged production ($25,000-$50,000), for established businesses scaling a proven concept; and full-cycle development ($50,000-$80,000+), for complex enterprise-grade systems. These ranges include architecture design, development, QA testing and deployment. Hourly rates range from $50 to $99 depending on role and seniority. Final pricing depends on technology stack, number of integrations and engagement model (staff augmentation, dedicated team or project outsourcing).
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How long does it take to develop a custom software application?
Development timelines depend on scope and complexity. At Pharos Production, a typical MVP takes 2-4 months, a production-ready application takes 4-8 months and a complex enterprise system can take 8-12+ months. We use an agile methodology with 2-week sprints, delivering working increments after each sprint. Every sprint includes a retrospective, progress report and planning session for the next iteration. This approach ensures transparency and allows businesses to launch faster by prioritizing high-impact features first. Get a timeline estimate for your project.
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What industries does Pharos Production serve?
Pharos Production serves 28 industries: FinTech, MiCA Compliance, Banking, Insurance, Crypto, Healthcare, Fitness, E-Commerce, Food & Restaurant, On-Demand, Manufacturing, Automotive, Energy, Oil & Gas, Supply Chain, Construction, Real Estate, Gaming, Streaming, Media, Telecom, Education, Aviation, Travel, Logistics, Marketing, Agriculture and Recommender Systems. Our deepest expertise is in FinTech, blockchain and healthcare, where we have delivered compliance-ready platforms (HIPAA, PCI DSS, GDPR) and high-load systems handling thousands of concurrent users. For the latest industry insights, read our guides on FinTech trends in 2026 and the Web3 technology stack.
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Why hire a software development company instead of building in-house?
Hiring a software development company offers faster time-to-market, lower upfront costs and access to specialized expertise without long-term employment commitments. According to Deloitte's 2024 Global Outsourcing Survey, 57% of companies outsource software development to access skills they cannot hire internally.
Factor In-house team Software development company Time to assemble 3-6 months (recruiting + onboarding) 1-2 weeks Upfront cost High (salaries, benefits, equipment) Lower (project-based pricing) Specialized expertise Limited to who you can hire locally Access to 90+ engineers across blockchain, AI, FinTech Scalability Slow (each new hire takes months) Fast (scale up or down per sprint) Long-term commitment Full-time employment contracts Flexible engagement models Risk High if key engineers leave Company ensures continuity and knowledge transfer For businesses that need blockchain, AI or high-load architecture expertise, outsourcing to a specialized firm like Pharos Production reduces risk and accelerates delivery.
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What projects does Pharos Production not take on?
Pharos Production focuses on mid-to-large custom software projects with budgets starting at $10,000. We do not take on template-based websites, WordPress theme customization or short-term contracts under one month. We also do not provide non-technical staffing (marketing, sales or design-only roles). Our strongest fit is blockchain, FinTech and healthcare projects where security, compliance and high-load architecture are critical. For smaller projects or MVPs under $10,000, we recommend exploring freelance platforms or no-code tools as a more cost-effective starting point.
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Why does Pharos Production use agile methodology?
We use agile with 2-week sprints because it reduces the risk of building features that miss the mark. Each sprint ends with a working demo, a retrospective and a plan for the next iteration.
This means clients see progress every 14 days and can adjust priorities based on real results, not assumptions. We chose this approach after years of experience showing that rigid, fixed-scope contracts lead to scope creep, missed deadlines and products that do not match market needs by launch day.
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When should you NOT hire a custom software development company?
Custom development is not the right choice in every situation. You should not hire a custom software company if: your problem is fully solved by an existing SaaS product (e.g. Shopify for e-commerce, Salesforce for CRM); your budget is under $10,000 and timeline is under 4 weeks; you need a simple landing page or marketing website (WordPress or Webflow is faster and cheaper); or you are still validating the idea and have not spoken to potential users yet.
In these cases, off-the-shelf tools or no-code platforms offer better ROI. Custom development makes sense when you need unique workflows, regulatory compliance, high-load architecture or competitive differentiation that packaged software cannot provide.
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What kind of projects has Pharos Production delivered?
Here are three anonymized examples from our recent delivery history:
FinTech startup - payment platform (MVP)
Scope: mobile app + backend API with bank-grade encryption. Team: 4 engineers, 1 QA. Timeline: 10 weeks. Budget: $38,000. Result: launched on schedule, processed $2M+ in transactions within the first quarter.Healthcare provider - patient portal (Full product)
Scope: HIPAA-aligned web platform with EHR integration, appointment scheduling and telemedicine. Team: 6 engineers, 1 DevOps, 2 QA. Timeline: 6 months. Budget: $120,000. Result: 15,000+ active patients, zero compliance violations in two annual audits.Crypto exchange - trading engine (Complex)
Scope: high-load matching engine handling 50,000+ orders per second, multi-chain wallet infrastructure on Ethereum and Solana. Team: 8 engineers, 2 QA, 1 security auditor. Timeline: 11 months. Budget: $340,000. Result: 99.97% uptime, passed three independent security audits.See more projects: NoMoreBets, Pulse, Sagas, Gambit Stream and Pleenk. For the full portfolio, visit our case studies. Learn more about the technology behind these projects in our guide to stablecoins and crypto infrastructure.
Dmytro Ihnatov is the Lead Backend Developer at Pharos Production. He documents backend architecture and research experiments from the team's work on a professional learning platform for aesthetic medicine.
