I don't know whether the following is related to the new rules and the DVLA are playing around with the website in preparation.
My pre-60 car still shows as MOT exempt on the general information section of the DVLA website and yet it now shows that it needs an MOT in the MOT history section.
Given that only "unmodified" cars are going to be MOT exempt on the 40 year rule I don't see how they're going to verify this by the implementation date.