Some stations, notably FRA, will let you know if you ask where you are on the list. They won't show you the list, but they'll tell you if you should wait or go ahead and board.

As we've discussed a few times here FRA delays upgrades until departure -30 mins. In my case this past week, they actually started boarding on time and at T-30 the entire aircraft had pretty much been boarded besides myself and the other four people who got their upgrades. If they didn't tell you then they'd have all of the people on the list waiting around only to have some not get the upgrade and then be forced to board last.