Now you ask I just remembered I flew on an A330 last month and had reserved seat 10J on NWA.com. I checked a few times in the week before my departure and I still had that seat reserved. However when I checked in online the day before my flight a different seat in row 17 appeared for that segment. I clicked to change my seat and found 10J was still available and changed back. Not sure why it changed - I have had that seat before or 10H and that did not happen.