You got wrong information from tier 1. By law, LPR must file AR-11 within 10 days of moving. By law, sponsor must file I-865 within 30 days of moving. It doesn't matter if there is an active case or there isn't.
It's not funny actually, because if mail gets lost, this means ROC extension letter, RFE, GC or other important mail can get lost too when sent to this address.