I don't think I'm letting anything in particular out of the bag, since Scott, CO Insider didn't have to tell me this while we were riding buses during last weeks' SMD2. CO does hold a few seats for last-minute purchasers of F seats, who were getting frozen out because of EUA. He only mentioned that they were holding up to 3 seats for this. However, he also told me that about 1/2 of the folks buying the upgrades were Plats. They were a little surprised by this as well.
I'm sure that revenue management watches all this and decides to hold off on EUA's a little longer in certain situations to see who'll bite and buy. I'm not one of those, as I've been lucky/early enough to get an exit row seat, and I'm happy to wait for an unpaid upgrade if I'm there, and I'm at about 80% with it happening at various time frames.
If folks want their EUA's early on, stop buying the upgrades. Othewise, youz takes your chances.