Many more items could be affected, and it's not just the IRS:
60-day rollover requirement, ability to get a document notarized (eg, spousal consent), distribution of SPDs to new participants, distributions of SMM's, due dates for 5500's, due dates for PBGC filings/payments, Annual Funding Notice, quarterly deposit dates, benefit restriction notice (eg, DB plans that fall under IRC 436 restrictions), reporting of PBGC events, etc.