Similar situation here:

Flying LHR-DEN tomorrow on a B fare and requested miles upgrade (15k) and have been on the waitlist since the day I booked.

Y looks to be completely full but there's more than 20 open C seats (confirmed with dummy bookings). Not sure why IM isn't releasing seats. I doubt there's going to be that many full fare business flyers less than 24 hrs to flighttime.

Since I'm a 1P on a B fare I should be towards the top of the list, correct?