[Ameiseuk]

I would agree with the comments on here - an MOT (whether is is the govt based system we have here in NI or a local garage in the UK) is a snapshot of a vehicles road-worthiness at that minute in time.
It is done by one person. That person may not remember all his/her training, may not remember everything that has to be done etc. May be under pressure if the last MOT took to long etc etc.

I've put countless cars/vans/trucks through an MOT/PSV over here and I've noticed that sometimes one or two items will be missed. Not checked horn on one test, could be fog lights on the next.

Generally though everything is covered and you have paperwork to prove it's road worthiness.

At it's last MOT the examiner picked up on a knackered bush which was causing shudder in the S8 at 70mph.
Tyre garage and mechanic were both convinced it was a buckled rim - eagle eyed examiner found a split bush and yet another bodged job by the previous garage.

For this I do have to thank Mallusk MOT centre