Put the car into https://www.check-mot.service.gov.uk/ and found these two advisories.
Advisory notice item(s)
Under-trays fitted obscuring some underside components
Engine covers fitted obscuring some components in the engine bay
I take it Engine cover could well just be a modified one to fit a pod filter, but what would be the under-trays? anyone know or have a guess?
I've seen that come up on quite a few MOT checks I've done recently, for various different cars (Jetta, Passat, Octy, A4 etc).
I wondered if it was tester-speak for "couldn't check [component] without removing parts". From what I remember there's a grey area regarding testing what's either present or accessible. I guess it's something to do with that. I didn't get the impression any of these cars were modified.