I know this is an old post but it's a useful topic to discuss if anyone knows the current "laws".
There are a lot of myths and grey areas surrounding the CAT / de-CAT. I "THINK" what you are saying about vehicles pre May 1995 not needing a CAT is from a manufacturers point of view. i.e after May 1995 manufacturers had to have a CAT fitted to their vehicles by law. However, i think if the vehicle is factory fitted with a CAT, it has to have it present for it's MOT even if it's pre May 1995.
Another grey area is being a JDM car, all FTO's are imports. At one time, imports wern't on UK MOT lists so they all had to be tested as de-CATS regardless. My FTO has passed previously with the de-CAT fitted. It has also failed with it. I think it depends where you take it. The times it's failed is when they test my car as a V6 Gallant because this is the closest engine to the FTO on a UK car. This really annoys me! Especially as once i had trouble taxing my car as the lady at the counter says the MOT and insurance documents don't match as one says FTO, the other Gallant
Best thing to do is say it's pre May 1995 and an import, then ask the garage how they'll test it. They're probably all different because they're not 100% sure them selves what's right and what's wrong.