Indeed there are only 3 papers for each subject. Traditionally, every year a new paper was produced and an old paper withdrawn. Quite often the same question will appear on more than one paper. When the CAA became short staffed the papers ceased to be changed annually.
When I became an examiner I was taught that I should debrief all ground exams,
if you are also the instructor, as many examiners are, you are going to refresh the areas that the student fails in. All the guidance says is that you should not give the students the answer to the specific question, i.e you don't read out the answer off the marking paper but, if its a fact that they don't know, you are going to reiterate the knowledge to them because as an instructor that's your job.
The CAA talks of standardising foreign examiners but has actually failed to standardise any of its own examiners over the last 12 years!