BGI has a large UK expat population and regular Christmas bookers, so my assumption is that the seats are being released in CW, but there will be a lot of competition for them. Those based in BGI have the clock on their side. This assumption is based on the fact that the SOP is for BA to release all the 355 seats in WT, WTP and CW at once at midnight GMT and it's either all or nothing, Moreover if BA add an extra flight, usually well under 355 days, then immediately there is an opportunity to snaffle difficult to get seats since the regular bookers won't be online when it happens. The extra MLE flights being examples of this. Here is the availability for the currently last date available, Christmas Eve 2022. There is at least one seat available in WT or WTP for all date shown from 19 December onwards.