As I understand the rules, MFU is available for booking up to 21 days before departure and a 1 sector upgrade on a 2 sector booking is permitted if the other sector has no availability.

On some routes (HKG for example) it seems to be the case that award seats in J are drip-fed into the system, as the relevant month approaches. I am wondering whether if 1 leg becomes available and I do an MFU, I can then MFU the second sector if that becomes available later, but at least 21 days before departure of the 1st sector (I assmue later would not be possible).

I am wondering whether anyone has successfully done this and whether my assumption on timing is correct.