I hadn't heard of variations on yearbooks, but they could be like the media guides. The team usually issued 2-3 versions of the yearly media guide: one to reflect spring training, one in June (mid-season) and one in August/September for late season. The earlier ones are more plentiful than the later issues. This was common for the team in the late 50's through the 60's and early 70's, back when media guides were for the media and not the general public.
You are absolutely correct as I look for that when I am finding my Cubs Media guides. I think one thing the Cubs did back then, which I why I remember reading something about the variations, is do one early Spring either just before or just after Spring Training began, then do another one just before the season started. I know there is a list out there, I just can't remember where I read it or found it. Thanks.