I use Avios all the time to book domestic legs but this is my first time using them to upgrade a BA flight. I have a friend that's flying to London over the Christmas break and has purchased for Club World tickets. The outbound segment opened up for upgrade about two weeks ahead of their departure, first three seats, then the next day the fourth opened up. On the return there seems to be wide open availability until Jan 1st, then everything just goes blank for the entire month. I show F9 on many of the flights the first few days on January.