Sorry, this is pure guesswork. Its unlikely they would use all new questions in their sample, and new questions are being generated at quite a rate in some subjects. If I am right (and I may not be) and you then put yourself in the UK CAA's shoes they would not want to do this too frequently in any one subject because it represents quite a lot of work. Far easier to just draw questions from the entire database - but then there has to be some method for printing out all the different exam annexes and making sure the candidates get the correct pile for the exam they are about to sit. Also the Authority have to rely on all the questions in the database being suitably validated, by their standards as well as by EASA's. I'd be interested to hear how the Authorities deal with Annexes in other EASA States.