I've had a number of problems with NW award tickets the last few years. My last one being just yesterday.

I was finishing my RTW trip, and had my last two segments on CO. I had changed from a DL flight about 4 months ago. A schedule change had been showing for two months on the last CO leg. I had called NW, and they said it was okay. (The schedule was just changed by 2 minutes).

I show up in SJO, along with some relatives, and the CO agent has my itinerary, but it is not actually ticketed. The agent goes off muttering "Northwest", and disappears for 20 minutes. When they look it up, it's still showing Delta segments I had 4 months ago.

I do get ticketed, but it's a large hassle. This same thing has happened at least once a year with NW awards.