Originally Posted by
zigenbock
I'm not 100% sure either, but I am sure someone will fill us in pretty quick. I have also done changes when Y only has a couple of seats left. I think that as long as they are selling seats, then you can do the SDC.
On PMUA, anyway, the flight must be booked to no more than capacity - 1, in the same class of service.
This means there are cases where they may still be selling seats (as they're willing to overbook via sales), but you cannot do SDC.