Thanks for the explanation! So let me ask another upgrade question. When I'm waiting on a GPU for a flight that I've booked long in advance, I often notice that as close to departure as two weeks, there are still many business class seats available, sometimes more than 50% of them, which gives me hope that my upgrade will be confirmed. But then it seems that most of these seats get snapped up in the last weeks before the flight. What's going on?