How accurate is "A booking that has already been part flown will not be upgradeable."? Does that mean if _any_ sectors are flown, it is ineligible (for example, the outbound of BUD-LAX return)? Or is it only the sectors on the current journey? (For example, BUD-LHR-LAX is flown, LAX-LHR-BUD upcoming, can I upgrade LAX-LHR from J to F using UUA? Would it be 22500 miles offpeak?)