A lot of RAG systems fail quietly after launch. The retrieval layer still returns relevant-looking text, but the corpus drifts away from the real world. Policies change, product docs move, records get corrected, and operational state turns over faster than the index. The result is a system that sounds grounded while relying on stale evidence.
Keeping RAG current is not a matter of running a nightly reindex job. You need an update mechanism that decides what changed, what needs to be invalidated, what needs to be re-embedded, and what should stay untouched so relevance does not bounce around every day.
Different source classes change at different rates, and they matter differently to the user.