If you deny a claim and we find other transactions that occurred a year prior to the transaction that was denied, that is from the same merchant, can the customer file claims on those for the same reason as the one that was denied? Hope that makes sense...:)

There is not statute of limitations for filing a claim of unauthorized transactions under Reg E. That being said, if based on your investigation, you determined that one of the recent transactions was not an EFT error, you can very likely use the same documentation to determine that all of the other transactions were not the result of an EFT error as well.