Just like some of the original Marshall's are a little different, because they were trying to buy what components they could in the UK with a war going on. Mark's inconsistency on the original CCV's was the same. Mark is a tweaker and builds from what he hears. There's probably not two of the same.
The CCV without any clipping, actually makes very minimal tube gain. Two tubes for each channel isn't going to bring about a large amount of gain. But, as Josh said, the overall tone with the clipping engaged is almost like layering the clipping on top of the cleaner, lower gain tube tone. This is what gives the CCV so much punch. And, the more you crank it, the tighter it gets.
All that said, I leaned toward Mark's modded Marshall's for the tone and feel that I wanted. Still, they are fine amps and indeed, most are different. And, there are going to be subtle differences in the production models over the originals.
Steve
and, if that is what you are after, then it is a good thing. 
