A few weeks ago my wife (MVPG) used 25k miles for a one-way OMA-SEA in late July. For a friend, Main cabin. Yesterday the friend asked her about an upgrade to Premium. When she went into the reservation, she was prompted to use a GGU for him - so she did and he's now in 2F. What was surprising was that the system prompted her to use a GGU. That prompting seems like something new; at least it's never happened for me. But it's been a long time since I tried to use a GGU other than at initial purchase. I know EF can help with using GGUs post-purchase, but I no longer fly enough to get much value from the tool.