The reality is that you are involved in a numbers game where the numbers aren't yet known.
ej don't know how many fo's will move to BA. Nor do they know how many internal pilot's will move to the new bases from their very good European contracts.
Advertising externally is also a lever for those who are undecided and ej know this. Especially so for newly qualified Commanders who may be offered a new base (with associated time freeze) and "if you don't seriously consider it blogs we have many DEC applicants ready to start"
There may also be pressure on numbers at individual bases where a/c are planned to be re deployed to the new bases.
Dumping somebody at an advanced stage in the selection may be a reflection of the shifting requirement. Sadly I doubt if those running the process give it a second thought.