Originally Posted by
WineCountryUA
It is my understanding, the standard procedure (not always followed) is for GA to come on-board and provide new seat assignments. No requirement (maybe a good idea) to make specific arrangements with GA. Have never hear of "once you board, you have lost your place on the UG list." Do you have different information?
Your understanding matches my experience, having received an upgrade while seated in E+ several times. Further, one time I was seated in an exit row with a companion and when the GA came to upgrade me, I declined, and she consulted her list for the next in line (clearly surprised I declined, and I have no idea if a new boarding pass was issued!).
I have never made specific arrangements with a GA prior to boarding.