Legal RAG systems often retrieve passages by semantic relevance, lexical score, or citation match. In versioned legal corpora, however, a passage can be topically relevant and citation-matched while being legally invalid for the operative date. We study law-in-force retrieval: retrieving evidence that matches the authority, is valid at the operative date, and supports the answer. We build LawInForce-eCFR from 805 human-validated eCFR/CFR amendment pairs and 3,220 controlled answer-flipping yes/no questions. We also present AuthorityFirst-RAG, a transparent diagnostic retriever that decomposes retrieval into authority identification, temporal scoping, and rule-support ranking. AuthorityFirst-RAG improves Recall@1 from 2.80% for BM25-date-filter to 30.90%, but generation remains difficult even with GoldOracle evidence. These results show a dual bottleneck in versioned legal RAG: retrieving the law in force and applying numeric legal rules.