What does ply exposed mean in practice?

I have a question on how the MOT Manual is interpreted with regard to tyre condition.

My car failed its MOT on the basis that plys were exposed on all four tyres. To put it in perspective, the tyres are Pirelli Scorpion semi-offroad in very good nick with about 4mm above the 'wear indicators'. Small cuts but nothing over 1cm.

Before dishing out on 4 new tyres and sending off 4 very useable tyres to be scrapped. I took it to a tyre fitter who could not find any cuts over 1cm. Then I took it to an MOT tester acquaintance for a visual inspection and he could see nothing he would pick up on.

So, I took it to to the MOT station it failed on and they very kindly showed me the criteria they use and allowed me to inspect failures.

They looked for sub-1cm cuts made by small stones and then levered open the small cut. The failures were on very small 5mm cuts. On two a single white ply cross section was visible in the cut wall when levered open. On one a 2mm 'top of ply was visible' deep in the cut. On the third no ply was visible - but a rust colour was there which I am told is evidence of a cut to the steel. This last cut was about 4mm at top.

The MOT guy said that represents ply visible according to the criteria.

I thought that cuts were covered by the 2.5cm guidance point. That the visible ply guidance was a separate assessment based on WEAR being visible to the naked eye without forcing open a small cut.

So I thought that one point excluded the other and they were separate.

It seems to me that a single ply cut by a small stone is not a safety hazard and the MOT tester agreed but said that things are much more stringent nowadays and that he (rightly) has a reputation to keep up. If this is the case then the nation will be sending a lot of hardly worn tyres to be scrapped.

So, are these two separate line items - one for 2.5cm cuts with ply visible and the other for wear? Or is it the case that they are combined guidance and that any ply showing no matter how small the cut and only a single ply means a failure? If so, what is the point of the 2.5cm guidance?