>>18736924This is my experience.
Back in the day, when playing Red, one time I got bored of cloning, missignoing and duping bikes I decided to go to the Mewtwo's cave and started to kill everything I found until every one of my mons died from Struggle. After a few KOs I decided to hit the Pokecenter and put my Hypno in the box to take Dugtrio I think. Later on, taking my Hypno from the box and battling my bro, I noticed the speed was sightly better, and I thought I "overtrained" it because he was already in level 100.
So, I wrote in a paper the current stats of Hypno and decided to go to the cave again and killed everything I found until he got 0pp on everything (trying to kill a Graveler with Struggle would take fucking years), deposited him, saved, and retrivered him again, noticing like 3 points more in SpA and 5 in Def and shit like that. I did the same thing until it stopped earning points, and did the same for everybody on my team and main box (Charizard, Blastoise, Venusaur, Mewtwo, Mew, Raichu, Dugtrio, Machamp, Jynx, Dragonite, Muk, Magneton, Omastar, Clefable and Starmie) and the process was similar.
Still have the catridge and I really never bothered about what the fuck happened with leveling those 'mons, but at least they saved my ass more than frequently in Pokemon Stadium.