I upgrade internationally on NW using CO miles all of the time just by calling and planning ahead. I'm not much of a rule guy so I just call and say - I need to go from SEA-AMS around these and I need a fare / date that I can upgrade with CO miles. 90% of the time it works out just fine. If not I then look at standard WBC award 90K to asia for instance, and worse comes to worse RuleBuster (EasyPass) award. But usually I only have to be 2-3 days flexible to get the standard upgrade. So, why take the chance - just call.