Gaps yes - was working on a Universal Cal. 481 yesterday and it's not listed in the E-O-G volumes, but there are some close relatives....I agree very nice to have if you service a lot of different vintage chronographs.
I'm surprised no one has listed the most common books I use yet - Bestfit. If you work on vintage, it's pretty much a "must have" I think.
So I would add "BESTFIT 111 Encyclopedia of Watch Material" and "BESTFIT 111A Encyclopedia of Watch Material" to the list.