We never did move up from our E- seats--the seatmap showed E+ completely full every time I checked, up until the night before, and at the gate things were no better.

Sigh. It happens. But somebody must have taken those E+ seats vacated by pax benefiting from UDU, right? So how, exactly, does UA manage that? Do they employ the same criteria used for UDU, or do they wait to see if E+ purchases at check-in fill any newly-vacated E+ seats before offering them to elites in E- seats?