Shawn,
It is my understanding that a check can be returned for faulty endorsement issues for as long as 3 years after it was negotiated. In some circumstances, this time period has been shortened to 1 year. However, if the person negotiating the check is the intended payee, this should not be an issue.
Reg CC and Reg J regulate the time period that a Payor Bank (the bank that is paying the check) has to return a forged or counterfeit check. Generally speaking the Payor bank must return the check by midnight of the banking day AFTER the banking day on which it receives the check.
I am not an expert on processing times for checks between non-local institutions. But generally speaking, depending on the local/non-local status of the Payor bank relative to the Depository Bank (the bank where the customer would deposit the check), I believe it can take up to five banking days for a check to go from the Depository Bank to the Payor Bank, and then another five banking days for the item to get back to the Depository Bank as a return. That is an extreme example, and more generally it takes 2 to 3 days with another 2 to 3 days for return. For local banks (banks that are in the same check processing region), it may be as quick as 1 to 2 days each way between banks. The easiest way to determine if the check you have is from a local or non-local bank is to ask your own bank. You can also look at the list of routing numbers in Appendix A of Reg CC. Within each Reserve District, there are check processing regions.
Reg CC - Appendix A, Routing Number Guide
This is one reason why Reg CC allows for an 11 day hold in extreme circumstances. That would be 11 BANKING days which translates to just over two weeks time.
So you can wait after the 11 banking days, or you can also try contacting the Payor Bank to see if the item has been paid. When you call the Payor Bank and ask if the item has been paid, you should also ask if the item is still eligible to be returned.
This is more the case with a private party check than a Cashier's Check. A Payor Bank SHOULD know if the item in question was a legitimate check. What can happen with a private party check is - the check comes in through the check clearing system and is paid against the account. Later that day, a levy comes in to attach available money in the account. The levy (and any number of other legal enforcement actions or actions by the account holder) takes priority over any checks which must then be returned unpaid.
It is my understanding that after the deadline has passed for the Payor Bank to return the check, it must now pay the check. The only reason the Payor Bank may still be able to return the check is if the endorsement was forged (for instance, if you stole someone else's check and forged their name to cash or deposit it), or if there are other obvious alterations on the face of the check (example: You received a check for $40 and put in an extra "0" to make it $400 and then cashed or deposited it.)
Again - I am not an expert in all of the backroom processing for check clearings, so if someone else can clarify what I've written, please do so.
Shawn - final comment - I don't know if you want to soften the harsh language aimed at banks on your website. While we should be used to this as much as lawyers are, we still cringe when all of banking gets labled with the "Bad Banks" brush.