I believe you can work this out using filters in Echohawk's Complete D&D Monster Index. In fact, Echohawk probably knows already; I think he has done number breakdowns like this.
For AD&D, after eliminating the duplicates, I count a total of 1987 unique creatures from all official sources. That includes 181 unique creatures such as demon lords or archdevils, so just 1806 if you're looking for generic critters.
An hour and a half of counting later, and I make the total for AD&D 2nd Edition 4316, of which 282 are unique creatures, so 4034 generic 2e creatures.
Well, that explains why I suddenly feel very tired.![]()



(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.