As I read it, the question is not about the bassinet seat location, but the physical bassinets themselves. i.e. if there are 6 bassinet positions, do BA guarantee to carry 6 physical cots.
There is some discussion here:
Baby seat (not bassinet)
From skimming that, the answer appears to be that they cannot guarantee it and it is first come first served, but it seems to be a pretty uncommon occurrence for one
not to be available in practice. Perhaps one of the helpful staffers could give a more exact answer?
EDIT: They already did while I was typing
