Review your state's version of the UCC Section 4-404.
The model version states:
"A bank is under no obligation to a customer having a checking account to pay a check, other than a certified check, which is presented more than six months after its date, but it may charge its customer's account for a payment made thereafter in good faith."
The bank generally has no liability if they paid a stale dated check in good faith if the customer did not notifiy the bank ahead of time.
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No, I didn't lose my mind. It got scared and ran away.