Hi all, long break here and lots going on (including my grandmother passing away last week) but I am back!
I do know the answer to the four theory papers each year - one is for March, one for June, one for November and one for Special Visits, hence the names A, B, C and S for the papers (these are the names of the sessions).
I am an experienced and highly qualified instrumental teacher, but still not experienced enough (or good enough at the piano) to become an examiner. It really isn't easy to become selected. They are all much more highly trained than I am, have usually played a variety of instruments themselves, played in professional orchestras, or been conductors or heads of music departments for many, many years. Believe me, they will know how each instrument is meant to work and sound, and that it can be hard to cross the break on some wind instruments, and difficult to play strings and trombone perfectly in tune early on, etc etc. We were required to learn lots about this for A level music, and Grade 8 theory, and examiners have much more experience than this. Being 'generalists' means that they mark on musical merit - accuracy, expression, style etc - but obviously they are going to know that fingering, breathing or tuning is harder on certain instruments. I can only think that if they all marked just their own instrument, the marks might possibly be slightly lower because they would be even more aware of every single imperfection, or know that a Grade 5 student 'should' be able to play in tune or cross the break effortlessly, for example. I would love to be an examiner one day, but am not sure if I'm getting too old to radically improve my sight-reading for the aural tests...
BTW I have only ever had one big shock with ABRSM results. The children normally come within 5 marks of their mock exam marks - usually improving a little between my marking (2 weeks before) and the big day. Trinity, I have only been using for a few sessions now, but so far they have been roughly as expected, except for a potential distinction last term who got a low pass. As all the other results were OK, I can only conclude that he messed up severely. He did look a bit jittery!