When Retrieval Is Not Enough: obsolete retrieved facts can degrade agent accuracy
arXiv:2610.36308v1 analyzes the single-hop FactConsolidation task in MemoryAgentBench and shows that retrieving the newest statement is not sufficient for correct answers. With Qwen2.5-7B-Instruct on a 6K-history setup, BM25 accuracy falls from 45% to 32% when the retrieved evidence budget increases from 64 to 512 tokens despite a gold audit finding the newest statement in each retrieved set; substituting an unrelated statement with an obsolete competing statement drops accuracy from 100% to 44.6% for Qwen2.5 and from 100% to 87.8% for Qwen3-14B (all 50 harmful paired flips were classified as stale), and a 32K-history replication shows BM25-64 outperforming BM25-512 (69% vs 58%).