I think the current setup for the SEs makes totally sense (ok, Volume 4 is debatable).Fair enough. Might I suggest to rework the content of each volume so that it makes more coherent sense. Like vol 1, can omit a few things like the solo strings or Appassionata extras, and finish off the winds section. Then vol 2, can focus on a more complete chamber strings or keyboards...etc.etc. Because there are volumes with scattered instruments, then ones that are focused on 1-2 instruments...I think there should be some uniformity about it. Just a suggestion (I'm sure it was mentioned before).
You will get all basic instruments of a classical orchestra with Volume 1, additional instruments and ensembles with Volume 2 and more strings with Volume 3.