How Rare?

Although I have electronic copies of its contents, I long ago lost or otherwise parted with my original Holmes boxed set. Lately, I've been trying to reacquire a copy of it and it doesn't look like it'll be hard -- or overly expensive -- to do. The problem seems to be that most of the copies I've found on eBay or through used game sellers include module B2, not B1, as I had when I got my copy back in 1979.

Does anyone know if the B1 version of Holmes was unusually rare? Or is it just that those who have the B1 version tend to treasure it more and thus not put them up for auction or otherwise sell them off? I'd really like to obtain a copy with B1, as it's one of my favorite modules of all time -- maybe even the top of the heap -- but it seems difficult to find for some reason and I'm curious as to why this might be.