If you ask them to inspect the car as a pre-mot then they can just like anyone can give the car a health check in between mot's.
I was always under the impression that whilst an MoT test is only once a year... the premise of the necessary standard applies all the time... and therefore in theory any responsible person who knows that a car doesn't meet that standard, would be duty bound to fail it... which could in theory even be the day after a new MoT had been granted if something had deteriorated.
That is obviously a really black and white way to look at things and I'm certainly not saying that I agree with it if the idea was to sort it in the first place... but I would imagine that's why some official MoT test stations would just do that as a matter of course to cover their own a55.
Whilst I can understand the sense of pride in a complete clean sheet. For me... I think I would almost value seeing a corresponding action with an advisory just as highly... maybe more so because I could clearly see it was cared for and addressed. It would only be if it was ignored for an extended period I would be worried. In some ways I would possibly be more suspicious of a car that had never had an advisory... because whilst in theory it could show good ownership, it could equally likely show cr4p testing. My Range Rover passed it's test clean last year... and a month later I had a decent specialist look over to assess a knocking and it needed a load of suspension work doing with some parts being described as being very much on their last legs... that didn't happen overnight so the garage who did the MoT clearly didn't spend much... if any time... checking... which is a tad concerning but kinda proves the point.