I've searched the forum and cannot find the answer to this question, so here it goes.

Going SLC-DTW and back starting this weekend. Booked through NW phone reservations because we had a NW ECV to use. Going to DTW we are on NW flights (NW1072 and NW 1448 on 10/10), but coming back we're on a Delta flight 10/14.

When I go to NWA.com, I can pick and choose the seats for the first two flights (to DTW), but cannot pick seats for the Delta flight back to SLC (there's no active link on the page where you choose seats).

When I go to delta.com, and bring up the itinerary, there's no link or option to choose seats for any of the flights. Also, on NWA.com, it shows our seat assignments (for the one flight we have assigned seats), but on delta.com all the flights say "Not Assigned" for our seat assignments.

At this point, is there any way I can choose seats for our Delta flight? When I do online check-in for the return flight, which site do I use, and will I be able to pick seats at that time?