The problem is that the more time goes on the more is discovered as to when pieces were actually written so you get more and more convoluted trying to renumber things. The solution they arrived at was a compromise toward simplicity mixed with comfort.
That said it's still pretty inconsistent in what it seems to keep in the main sequence vs the appendix as far as works that are doubtful goes, or what constitues enough enough a piece to get assigned a number vs keeping is as just a sktech...