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Dragon magazine refered to the 1981 edition of D&D as either “Second Edition, Revised” or “Third Edition”. (The 1983 edition was sometimes called “Third Edition” or “Fourth Edition”.) The 2000 edition should’ve been called “D&D Sixth Edition” (leaving “Fifth Edition” for the Cyclopedia era edition) or “AD&D Third Edition”.
The description for the spell Detect Invisible spell is missing (or invisible?) from the 1981 Basic Rules.
The 1981 Expert Rules list lower Saving Throws for Dwarfs & Halflings than does the 1981 Basic Rules or B2.
Earlier printings of the 1981 Expert Rules say “Edited by Dave Cook”. Later printings say “Edited by Dave Cook with Steve Marsh”. (Dave “Zeb” Cook would go on to be the primary force behind AD&D 2nd edition.)
According to the 1981 Expert Rules, clerics cast reversed spells by casting them backwards. It would appear that the decision to cast the normal or reversed version was made at casting time for clerics.
Early prints of the 1983 Expert Rules were compatible with the 1981 edition. Later prints, however, slowed down certain progressions (thief skills, spells, &c.) in order to “make room” for advancement through 36th level.
The correct (pre-Tolkien) plural of “dwarf” was “dwarfs”. D&D’s following Tolkien’s use of “dwarves” was unusual at the time.
D&D/AD&D crossover trivia: Supplement IV: Gods, Demi-gods & Heroes had a section on REH’s Hyboria. Deities & Demigods did not, although it include HPL’s Cthulhu, Moorcock’s Melnibonean, & Leiber’s Nehwon mythoi. According to Jim Ward (as posted on Dragonsfoot):
At the time we were writing that larger product TSR was working hard at getting the Conan role-playing game. We thought we wouldn’t need to cover those characters again because it was going to be done in the Conan Boxed set.