Having watched them for a while, I think that there are differences between Authorities as to how they draw questions from the CQB, probably dependant on the exam software they use.
I understand that some draw exams from the entire CQB, and that would mean that two candidates sitting the same subject on the same date would have quite different exams and quite different annexes.
Some Authorities seem to draw a sample of questions from the CQB, no idea how many, say 200 a subject, do their own validation on those questions as far as they are able, then select the questions for their exams from their more limited sample. This would mean that all their candidates have similar exams, with the same questions coming up repeatedly and the same annexes. I think the UK CAA do this, and choose the newest questions for their sample. Presumably they change the sample after a period and a whole new batch of questions arrives.
This is speculation only, based on the feedback we get.