T. Foster said:
Players in 1E AD&D were actually allowed/intended to read the Monster Manual. There are numerous "in milieu" passages in the descriptions that seem aimed at players as much or more than DMs (and the famous lie in the dark elf description -- stating that they are only legend). Plus, there are numerous direct references to the MM within the PH. And, last but not least, the cover blurb and introduction of the book itself -- "an invaluable aid to players and dungeon masters alike," "some DM's may wisely wish to forbid their players from referring to the MANUAL in the midst of an encounter" (emphasis mine). Compare to the in-no-way-ambiguous language in the DMG: "As this book is the exclusive precinct of the DM, you must view any non-DM player possessing it as something less than worthy of an honorable death." (DMG, p. 8).