The travel agent (Trailfinders) say they have no idea what the "DO" marker is so cannot do anything. BA say they can't upgrade the itinerary due to the "DO" marker! Is there another phrase or keyword I can say to them or to BA which will allow them to do the necessary and allow me to process this upgrade for my parents? It is an all BA itinerary and a standard fare booked in PE (T class) so should be upgradeable