Why is that strange? In your above example, you would have switched to Blue Extra on a flight that would have cost a newly booking passenger $1,000. Your underlying fare would not have changed, you booked Blue Extra for $200, and they’re moving you to a new flight, but the value of your ticket is still $200. If Mint is pricing at $1,500, yeah you would still only get $200 of paid fare toward that new ticket and would need to pay $1,300 to upfare. The reverse would be strange: an airline not only providing you with accommodation on a more expensive flight, but also awarding you 5x what you originally paid toward the value of a new ticket.