Garys first pokemon in gen 1 was a eevee. Its been like that ever since pokemon was created. Same reason how they tried making pokemon yellow a copy version of gen 1's anime.
I remember this extremely well. And OF course! The new audience. How can i completely forget! Best excuse ever, seeing how they twisted yugioh to the best anime to its worse. What else is next? Dbz? Bleach? Full metal?
Gary never had an Eevee in Season 1. I know this for sure because I just watched the Kanto arc again a few months ago.