Again, I'm talking in general terms here as opposed to specifics - I can't speak for every firm - but these will probably be approximate numbers, usually either based off the quoted number from the firm (which will be a general number which they give for general indications) or an average of confirmed intake numbers or something like that.
In terms of the exit interview example, this was just an example and won't be a rule by any means. I think an otherwise-perfect candidate would need to utterly crash and burn in an interview to be rejected purely on that basis in most instances.
