It's not going to be the answer you were hoping for, but yes, you must put forth some documented effort to identify all of the persons who conducted the transactions.
Click
here and scroll down to Administrative Ruling 92-2. You will find phrases indicating the bank:
“...is encouraged to make a reasonable effort to provide the information called for...Such efforts could include a search of the institution’s records or a phone call...to identify the persons that conducted the transactions. Administrative rulings have force of law. This one may be dated, but it has never been repealed and the underlying rationale offered for the conclusions it draws are still relevant.