Anytime there is not a VDP posted it is because there is a low close in obstace or an excessive descent gradient that prohibits the terpster from publishing a VDP. This didn't use to be the case. Somebody correct me if I'm wrong, but I think the fact that the terpster is required to give a VDP if possible, was new with change 19 to 8260, the terps manual. That being said, I imagine there are IAPs out there that were terps'd prior to change 19 and haven't been reviewed since. So they may not have a VDP simply because when the IAP was made the terpster wasn't required to provide one. Since I can't tell the difference, I always assume that if there is no VDP provided it's because of the first reason. I still calculate my own VDP but I'm even more cautious not to descend early.