Coriolis is correct, there have been two assessment days at FTE already. One of the ladies said not to expect a response until Feb regarding the BA HQ stage. I won't share any of the specific details of the day as to not compromise the integrity of the process.
I was doing a few calculations. FTE are running their assessments from 16th Dec to 17th Jan inclusive. That gives approximately 20 or so feasible assessment days. Given that they are assessing 16 per day, that means they invited between 300 and 350 to stage one.
We were also told what EB747 said; if you're good enough at this first stage then you'll make it to BA HQ. Only thereafter are the places truly limited.