Whew, I don't know, 2e had multiple products a month for a LONG time between the different campaign settings (Birthright, Greyhawk, Ravenloft, Plancescape) and heavy, heavy Forgotten Realms support and the PHBR series plus things like the Character screens and kits. There were a lot more adventures than people realized. Then the DMGR series. 3e we had 2 a month I think it was with support for setting limited to Eberron and Forgotten Realms. It might be pretty close though. I know for a short time we were getting two books, either generic or FR/Eberron and an odd adventure or map pack towards the tail end when they brought back the adventures more seriously. The tail end of 2e after the WOTC buy out we had FR, Greyhawk, Dragonlance, plus generic materials like the Monstrous Arcana and Monstrous Manual Supplements.
Thac0 was a headache, though.
I NEVER got THAC0, ever. For every character I played I had to write out a full to-hit chart for it to make sense, and updated the chart on my character sheet every time I got a THAC0 improvement on my character.
Aurora's Whole Realms Catalogue. Officially made as a Realms product, but overall an awesome D&D book in general. It's the absolute best "book of stuff" for D&D. It's not about weapons and armor, but the zillion other everyday things that you might want to shop for in a D&D world, in a very period-looking book that intentionally evoked the look of a 19th century Sears Catalogue, with prices and descriptions for everything you could imagine. Even 30 years later they still have never even come close to topping it as an equipment guide for D&D.
You know the much maligned sanitization of the game was very short lived. When did the Outer Planes Appendix come out? I think 90 or 91? It was before the compendium was changed to Monstrous Manual. I always thought Ta’anari and Ba’atezu, Yugoloth, were much more evocative names myself than Type 1 demon etc.
Aurora's Whole Realms Catalogue. Officially made as a Realms product, but overall an awesome D&D book in general. It's the absolute best "book of stuff" for D&D. It's not about weapons and armor, but the zillion other everyday things that you might want to shop for in a D&D world, in a very period-looking book that intentionally evoked the look of a 19th century Sears Catalogue, with prices and descriptions for everything you could imagine. Even 30 years later they still have never even come close to topping it as an equipment guide for D&D.