yes.
seniority numbers are only used for the cabin crew and flight crew communities in BA - the flight crew having their own, specific seniority system.
when you start, AMS-LHR, your seniority number will be around the 14,500 mark.
say on your course there is emma, bob and james.
emma is a major swat and her overall mark for her course (SEP; customer service; AVMED etc) is 98%; bob did very well, but not as good as emma and got 90%. james on the other hand did the 'worst' out of the entire training course of 20 people and scraped by with 80%.
their seniority numbers will be issued as follows:
emma (1st) - 14500
bob (2nd) - 14501
so and so (3rd) - 14502
so and so (4th) - 14503
so and so (5th) - 14504
etc, until:
james (20th) - 14519.