I am confused about the upgrades to D1 being available when there is Z class inventory. What if there never is Z class available, but there are still plenty of open seats? Will they wait to upgrade to D1 within 24 hours, or leave those seats empty? I'm looking at flights that I purchased PS for, that have 25 seats open in D1. No doubt it will get fuller as time gets closer, however, I don't see many flights at all for that route that have Z class available. The route is SEA-AMS.

I also don't see any indication that I'm on the waitlist, though they claimed to have put me on there. Perhaps it's not something I can view. They also claimed that they put me on the waitlist for the second leg, AMS-NBO on KLM, and told me that I had to call Delta 24 hours before the flight to try to get upgraded on KLM. Is this accurate information that they gave me?