You would only have up until your midnight deadline to return the item as stale dated so that idea won't help you. The depository bank would have no liability since a blank payee line essentially turns the item into a bearer instrument. The UCC allows an account holder up to 1 year to claim forgery from the date an item cleared the account, although some contracts reduce this timeframe.
The question boils down to, did your customer sign the check or is it a forgery? If you determine that it is not a forgery in spite of the claim, then you deny the claim. (The customer has the right to file suit for damages, bring in the handwritting experts, etc.) If you determine that the signature of the front of the check is, in fact, a forgery, then you reimburse the member for honoring a check that was not properly payable.
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