DMH, those are interesting questions. I'm not sure I've ever worked out how many unique AD&D or AD&D2 creatures were published.
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.
For AD&D2, I'll need to spend some more time eliminating the duplicates to get a total -- 2nd Edition tended to repeat creature a lot more than 1st Edition.