Steve M:
Your observations are correct. I have been following CO/NW for ASIA for at least 6 months and can tell you it changed about 4-5 months ago. Prior to this time there were seats on NW in the CO code share line on ITN. There have not been for the past several months, and indeed, if you look at EWR-SIN next July, there are still none. Complicating the picture is the fact that if you go to the CO website and punch in the dates it will quote a fare ($2,300) RT in coach on days that ITN says there are zero seats in any fare bucket, B/C or Coach.
The real confusion comes in when trying to get award seats or upgrades to ASIA. Both free and upgrade seats APPARENTLY come out of NW's "D" fare bucket. Technicaly, there is no such thing as flying CO to NRT and connecting to a NW flight to SIN/BKK, and being upgraded using miles in your CO account. If you want to go EWR-BKK, CO will sell you a wholey NW ticket and upgrade you with miles from your CO account, PROVIDING there are seats in the NW "D" bucket available. The actual NW tickets issued say "C" class. The only way to find out in advance if there are upgrade seats available without spending a huge amount of time on the phone is to go to the NW website and the Worldperks section. There you can search, day by day, for avaialbility of free Business Class seats to you destination. If these are avialable (and I believe this represents NW "D" seats) then there are upgrades available.
The question that is most confusing is what the CO agents really see on their screen. Do they actually see the NW "D" bucket or the "D" bucket on CO codeshare flights that we see on ITN. I have the feeling that they may have access to both, but typically only look at the CO codeshare seats. I can say that I was recently successfull in buying a seat JFK-TPE FROM CO on NW all the way and upgrading using CO Miles, meaning that in order to do th upgrade, CO had to be able to see the NW "D" seat bucket. It is very confusing, to say the least.
Note that it HAS been know for rookie CO agents to sell a seat on CO to NRT and onward to SIN/BKK. This is preferable since Business First service is far superior to WBC. Any agent that really knows the rules will only sell a NW ticket in these cases. Even the Intl reservation agents are confused when they get a call from someone wanting to go ewr-sin. If so inclinded, this can be used to your advantage.