I don't claim to be a NACHA expert by any means, and would appreciate some help on this one.

Customer has unauthorized ACH 7/15/08
Statement cut and mailed 7/31/08
Customer completes WSUPP 8/26/08

Section 8.6.2 of the NACHA rules state that a receiver must deliver to the RDFI a WSUPP within 15 days from the date the periodic statement is made available. However, I was always undert the impression that NACHA rules allowed an entry to be returned if it was done within 60 days of the transaction date.

What am I missing here? Am I confusing two things? Did the 60 days period get removed when I wasn't paying attention?

It's a two-part requirement. The WSUPP is supposed to be completed by the customer within 15 days of statement delivery, and the bank must enter the adjustment claim (send the item back) so that it's received by the ODFI on the first business day that follows the 60th calendar day after the Settlement Date of the item being returned.

Depending on the coincidence of dates, there can be a long time between the 15th day and the 60th day. But consider an item with a Settlement Date of 8/15/08 that first appears on a statement that is sent or made available on 9/19/08 (as you can see, there is some delay time built in there for processing the statements and getting them delivered). The customer would have until October 6 (the 15th day is a Saturday) to deliver the WSUPP. But the bank only has until October 15th for that returned item to be in the hands of the ODFI. That means the bank has to react to the WSUPP and get things wrapped up and out the door pretty quickly. I count about five or six business days.

For whatever it's worth, the WSUPP doesn't go anywhere unless the ODFI challenges your return or you are audited. The date you put the item into your ACH return adjustments can be controlled by the ACH operators. But they can't tell when the WSUPP was signed unless they look at it. I cannot advocate playing fast and loose with rules here, but I do know that the 15 day rule is ignored fairly often if the return can make it out the door on time.