I think this is finally complete enough to share: I've put together a tabbed spreadsheet documenting major Sears and Atari 2600 game manual variations. Sites like AtariMania, AtariBoxed, and VideoGameVariations are all extraordinarily useful, but I don't believe anyone has aggregated info on manuals like I've done here. There wasn't a whole lot of variation going on with 5200 and 7800 manuals, but the 2600 is a different beast altogether. A perfect example: including foreign language manuals/supplements, Combat has at least 8 major variants.
No, I'm not crazy enough (yet!) to track minor manual revisions...
Anyway, as esoteric as the subject of Atari manual variants may be, it's still a part of video gaming history. There have been many recent/ongoing efforts to preserve and document information relating to old consoles and games, but I feel like Atari hasn't received nearly the level of attention as some others. Certainly there are a number of online resources for Atari information already -- a few of which I named above -- but there's still lots of room left on the internet!
I'll be continuing to add links to images of the lesser known manuals as I have the chance. Please feel free to message me here or email me (address is at the top of the sheet) with images of uncommon manuals to be added. I may eventually also extend this to cover manuals for third-party 2600 publishers and 5200/7800 manuals, but for now it's being limited to just 2600 Atari/Sears.