I tried looking at a reservation that I have in Nov and get the following message:
Customer Advisory: We are unable to process your request. No changes have been made to your reservation. For assistance, please contact Northwest at 1-800-225-2525.

Maybe the problem is that only the outbound flights have seats assigned -- haven't reached the 89 day window for the return yet. I did call the elite desk and get an exit row seat for the domestic and an aisle on row 11 center for the DC10, where there are no favorite seats.
tom