I seem to recall some verbiage that under the contract of carriage you are never guaranteed a particular seat. Thus despite your advanced seat assignments, I think the airline would be within it's rights to give you two non-adjacent seats.
Originally Posted by tofromord
On a long flight (or any flight) where I would like more room to sleep, stretch, etc. does NWA allow you to buy 2 adjacent seats? Can I be sure the seats are adjacent? Do you get any mileage credit for the 2nd seat?
TF