This was my first DL-associated Amex card. A DL Reserve. I am a NW transplant.

@ Evan!
Thanks for pulling up the offer. It is a little vague on the "retroactive" part, but in an e-mail promo for the Amex reserve card it said "retroactive". This actually came up twice with DL agents, as they initially denied retroactivity.
I guess by now DL has some experience with people requesting the mileage credit.

For me it was really worth it. Earned enough for a TATL upgrade with the promo - if I could afford an M class ticket.