The modern Critical Text (CT) of the New Testament in Greek relies on the primacy of two manuscripts, the Vaticanus (B) and Sinaiticus (aleph). These manuscripts are said by the CT supporters to be older than manuscripts in the Byzantine tradition, and were not victims of scribal changes and accretions over the centuries of copying.
Statistically, we have to ask how many manuscripts were in use in the fourth century. Do we know this? I don't think so. We also have to ask how many manuscripts in use in the fourth century were in the Byzantine textual tradition, and how many were in the Western tradition. Do we know? I don't think so. I have never seen hard numbers for either statistic. The reason we need to know this is to determine if, statistically, our two extant manuscripts B and aleph are a representative statistical sample of all the manuscripts in use at the time.
What I am particularly interested in knowing is the ratio between the Byzantine manuscripts and the Western manuscripts. Particularly, I'd like to know the derivative, to know the rate of change over the centuries. Is it constant? Did one manuscript tradition start out dominant, to be supplanted by another? Are there oscillations back and forth?
What I'm trying to say is that I know, basically, that there are two extant manuscripts from around the fourth century which are given incredible weight in textual criticism, but I have never heard anything about the context for these manuscripts. Why are these minority manuscripts given so much weight? They are a tiny minority in the textual tradition.
If someone could show that these manuscripts are a statistically valid sample of the manuscripts in use in the fourth century, then I would agree they are important. I'm not sure anyone has ever done that. Textual critics have said these manuscripts are older, but they have never - that I have ever seen, please correct me if I'm wrong - showed what proportion of Western texts were in use in the fourth century versus the proportion of Byzantine texts, so they have never demonstrated the validity of giving so much weight to these manuscripts.
Again, my only conclusion is that we may never know. The only thing I know to do is have a King James Bible in one hand and a modern translation in the other, and compare them.