Thanks! I went ahead and submitted the mileage credit request. I got the generic screen that this will be processed and that I'll be informed via e-mail.

And yes, the ticket was reissued at some point because I got caught up in the "snowstorm" at JFK two weeks ago and was booked on different flights the following day. But this didn't impact on the return flight and the reissued ticket had the same info, i.e. DL flight, operated by VS.