Possibly, I suppose. But Puzo might have mentioned that had it been the case - it would have been an interesting note to add, wouldn't it?

And why leave it that way to possibly confuse the reader?

What I'm saying here is that there were places where the book was sloppily written, and Puzo's failure to name the sixth family may have simply been another one, especially considering all of the times he took pains in his writing to indicate that there were six.

There were several other inconsistincies in the book besides the two I cited.

One of these days I'm gonna go through the entire book with a fine tooth comb and find them all and write a post about it.