This is a question for Greg, or others from "back in the day" of Dave's early campaigns.
There is a discussion on DF about the first ever critical hit and/or fumble chart:
http://www.dragonsfoot.org/forums/viewt ... 11&t=71701I can't recall exactly when my group brought critical hits into OD&D. As long as I can remember a natural 20 has been a critical hit and a natural 1 a fumble, but I can't recall where we got the rule or when we brought it into play. I think that EPT had a crit rule as early as 1975, but Gary and Dave came up with so many rules early on and I wondered if anyone had a more definite answer to this.