I just "played" this game earlier this summer and "won," (sort of) but by luck. I called NWA Elite line almost every day to check on when seats were released. I started at the 331 day mark and kept at it. I was looking SBN-AMS/OSL. I never found seats all the way to OSL and ended up booking FWA-LGW and will take another airline to OSL.

The DTW-AMS flights run very full and are very popular. I was told, looking DTW-AMS that it was the "flight across the water" that was the issue in why I couldn't get seats. I'm not sure if the seats on those flights were ever released. We had to find the less-travelled DTW-LGW route for our seats. Even then, an agent told me I was getting the "last two seats" on that flight. However, two weeks later, my sister was able to cash in miles to get another seat on the flight.

I think they're released incrementally and (apparently) randomly. Persistence and creative rewards! There is a nice thread on here on creative ways to cash in miles for NWA across the Atlantic, using the many partners. It certainly depends on which agent you get when you call NWA too.