You've obviously not seen a "modern" VW diesel on a MOT emissions test 🙄.
I've used the same family run garage for years and when my 2011 Caravelle was tested, I was initially puzzled when we did the smoke test. When you apply full throttle when stationary, the maximum revs are about 2k rpm. They simply won't rev any higher. However what is noticeable is the engine sound and response when you press the accelerator pedal; it sounds like the injection timing is altered and possibly even the turbo boost, certainly the throttle response is subdued. Emissions are well within the required range