Does anyone know the current rules for upgrading NW international flights with CO miles? co.com doesn't list the rules any more, as far as I can see. It used to be that NW Y or B fares were upgradeable with no copay using CO miles. That matched what could be upgraded using NW miles. Since March 2009, NW seems to have started allowing NW Y, B, or M fares to be upgraded using NW miles, which matches the former DL rules. (See http://www.nwa.com/worldperks/travel/compan.shtml.)

So, are NW M fares now upgradable with CO miles, or not?