In general, it's one year, but it will depend on the UCC of the state in which the banks are domiciled. The paying bank has a statute limiting the period during which its depositor has a claim of duplicate payment (essentially, it's a claim that all but the first payment of a check are unauthorized), and that's dependent on that bank's deposit agreement and the UCC of that bank's state (typically 1 year, but some states have a shorter period). As depositary bank you make presentment and transfer warranties for up to three years, but a warranty claim against you would fail if the paying bank's customer didn't have a valid claim against the paying bank.
Problem is, if you are charged for the checks, you'll have a hard time getting it back, and it may not be worth legal action to recover.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8