it sounds like things were pretty screwed up (in terms of weather) yesterday. They should have had an agent go to the gate or had an announcement made or something, regardless.

If you had an e-ticket and the NWA ticket counter guy said "yes, take AA", you should have had him book you on the AA flight with a printed, endorsed version of your real ticket (or a "flight interruption manifest" voucher) so you could have gone to the AA gate with that.

Both you and the agent were probably frazzled, so this piece of advice is just an F.Y.I. for next time.