It's kinda funny how despite Genwunners being a thing, not many document how Gen 1,2, and even some 3 mons got redesigned over the years, largely due to GF not sending design docs to the anime fast enough until Gen 3
For instance, Sugimori intended Clefairy to have schlera. His digital art for the 1997 OST confirms it
interestingly Togepi isn't meant to have schlera, the lines are strictly for meek cuteness
Though for Gen 2 oddities we have
-many sprites not updating palettes from 1998 data (and even some sprites given Skarm), except Celebi. Sneasel was the most affected, and Spinarak's palette is weirdly colored depending on lighting conditions
Ironically, Celebi wasn't distributed well in GSC, so not many would even see it
-Green Chikorita is sadly based on the anime having very little info on GSC mons when they started dev. It's based on its 1997 SW colors, before the GBC was a thing. Though despite being yellow in 1999 art, the following year for Cystal it was changed to green due to heavy merch pressure and uniformity
For gen 3, not many were changed. It was most starters for proportions, and Torchic's microscopic gender difference
Personally, not a fan of most changes. The only positive one was Eevee getting a white tipped tail after 1998, and Tochic's spot, but the rest either get toned down (4 fingers, fangs, spikes), or get dollified/big headed, or tubby (most starters, Nidoking)