Former airline staff here who understands how airline reservation systems work. When you enter frequent flyer number into the booking, the system will validate your membership with the airline you hold the membership with and will 'pull in' whatever status you are at that particular time. If during the life of the booking your frequent flyer status were to change (up or down), the reservation system cannot recognise that and will for ever reflect the status which was relevant when the frequent flyer was entered for the first time. However, there is a way to overcome this by removing the frequent flyer number from the booking (airline staff can do that routinely, if requested), and re-apply the frequent number. In the process of re-applying the frequent flyer number, the system again validates it and pulls in whatever status is relevant that particular time.