In my experience whenever you are waitlisted they will always get your confirmation before changing your confirmed booking (whether it's change of class or change of date).

I'm guessing they would have held that seat unless a higher-priority person comes along.

It often seems to be the case these days that upgrade/award tickets are met with a "waitlist" answer. They seem to like to hold you there for a while and probably think you should be grateful as they're doing you a favour.

It is an annoyance that they now seem very conservative with inventory management. They seem to harbour a hope that they can sell seats at the top price (ie out of a particular bucket) and will happily leave you languishing in a "wait list" for weeks until just before the flight. It's not really a list as such - it seems there is some sort of periodic review so even if seats become free they won't be released to the lower buckets. For example I was waitlisted for a December flight (L Elite on a ticket that was open) some 5 months in advance and was told that really I had requested too early and that nothing would happen until much nearer the date. In the end the only way is to "push" them (preferably using a Chinese speaker as those with the authority to do anything typically don't have the English skills). I can understand their wish to prioritise high-price buckets over cheaper ones/upgrades - but I'm talking about situations where it is plain there is plenty of availability. My last upgrade request Elite to PL didn't clear by about 3 days before the flight after waiting 3 weeks. I cancelled it because I was fed up. Guess what? PL was half empty - and I was OP-UPed anyway, so their approach cost them.

Glad it worked out for you.