Great advice here. Look for anything that cannot be independently verified - cash deposit, phone call, etc.
One bank, they had an intermediary step between active and dormant where the bank automatically sent notifications to customers. Also - state specific rules - in some states, activity on one account (if linked to other accounts) would be considered active. (If I had a savings and checking, as long as e.g. the checking account was active, the savings would not be considered dormant, especially if they were receiving statements at the same address.)
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Integrity. With it, nothing else matters. Without it, nothing else matters.