The recent decline in the international upgrade availability has been a much-discussed topic. I soon will be its latest victim.

I have a leisure trip from EWR to PVG departing in a few weeks. I currently hold a discount ticket, and am looking to upgrade using miles. Unfortunately, there are no D fares currently available, however there are plenty of WBC seats available in the form of C fares. My question is, does the C seats eventually gets released to D? If so, are there any patterns?

Looking at the number of seats available and the close proximity of the departure date, I can't imagine NW selling all those seats. Will NW's deny upgrades using miles even if it means flying with empty WBC seats?