Let me provide an example to help you separate these issues.
Let's say that I receive a check payable to Brian Crow in connection with winning the UK National Lottery (obvious scam and the check is counterfeit drawn on your bank.)
Now lets say that Joe Thief stole my UK Lottery Check and either forged my signature or just wrote For Deposit Only and deposited the check payable to me into his account. Even if I discover that my check is stolen, I am precluded from trying to make a forged endorsement claim, because the check on which my endorsement was forged was not a properly payable check since it was counterfeit. Therefore there will never be a valid reason for returning a counterfeit check for a forged endorsement. Your responsibility to your customer is that you only honor properly payable checks, which you did not do, and the UCC only gives you to your midnight deadline to return them.
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Sola Gratia, Sola Fides, Sola Scriptura, Solus Christus, Soli Deo Gloria!
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