Weird. DFAS Retropayments says they do not know why I was "credited". They have 7 days to explain or provide an answer. Meanwhile, I've got a check that I should not cash.
I did the math myself and figured it out. It looks like they paid me retirement for JAN and then added on top of it what my VA payment would have been in JAN too (CRDP). I have not done 20 years and I am not authorized CRDP as far as I can tell. When I add those two figures it comes to the EXACT amount (down to the cent) that DFAS made the check out for. I called and they said they would need to take a week to confirm what the credit was for because the technician that entered it did not list the payment as CRDP.
And now we wait...