First, you must know that "clinically definite" only means "the best that we can do", with it in mind that no specific MS entity means no MS diagnosis is beyond reproach. For proof, you only need to look at the past and diagnosis which have been turned around after the fact and look to the many people on thisisms who are "in limbo" because no one can tell the with certainty whether they do or don't have MS. The uncertainty in MS diagnosis is certain.
It really doesn't matter how large the "in limbo" group is since they are clearly not CDMS. As for the group whose diagnosis has been "turned around", your argument would be stronger if we had any idea how large that group is. Recently, a case was posted on TIMS where MS was called a misdiagnosis after the problem was found to actually be a vascular issue that now looks like garden variety CCSVI. I hear stories of people diagnosed with MS who actually had Lyme disease, but I haven't heard any specifics on that so I wonder if that's more urban legend than anything else. My point is the actual percentage of bonafide misdiagnosed CDMS could well be very small.
It appears very likely that the study going on in Buffalo will affirm Zamboni's finding. All but a couple of people who have seen Dr Dake have had stenosis. Dr Simka is finding the same thing. No one has any idea the percentage of misdiagnosed CDMS. So the most likely explanation for this 100% paradox, is that the rate of misdiagnosed is actually not that big.