Treasury follows the Green Book (they wrote it) and I'd be guided by the Green Book if I were you. Once you have received a DNE, you are required under Treasury regulations (and the Green Book) to return any and all federal recurring benefit payments received via ACH after you've learned of the death. You aren't required to return direct deposits of such funds received before you received that notice (or some other documentation of the death).
It's complicated, but follow the Green Book.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8