Thought I’d chime in with some data. In the first week of this year (1st January to 8th January) 149 cards belonging to the Pokemon Game set had their totals changed, of which 62 are 1st Edition-stamped. The following Base Set PSA 10s were added to PSA’s population report:
1st Edition (PSA 10 changes)
1x Machop (Pokemon Game 1999 - 1st Edition)
1x Magnemite (Pokemon Game 1999 - 1st Edition)
1x Rattata (Pokemon Game 1999 - 1st Edition)
Unlimited (PSA 10 changes)
1x Mewtwo-Holo (Pokemon Game 1999 - Unlimited)
1x Venusaur-Holo (Pokemon Game 1999 - Unlimited)
1x Charmeleon (Pokemon Game 1999 - Unlimited)
1x Abra (Pokemon Game 1999 - Unlimited)
1x Magnemite (Pokemon Game 1999 - Unlimited)
1x Onix (Pokemon Game 1999 - Unlimited)
3x Pikachu (Pokemon Game 1999 - Unlimited)
1x Ponyta (Pokemon Game 1999 - Unlimited)
1x Lass (Pokemon Game 1999 - Unlimited)
1x Energy Removal (Pokemon Game 1999 - Unlimited)
No Shadowless cards or foreign (Pokemon Game 2000) cards have appeared during this timeframe.
Focussing specifically on 1st Edition, these are the total changes for each of the cards which had at least 1 new entry:
1st Edition (Total changes)
3x Alakazam-Holo (Pokemon Game 1999 - 1st Edition)
4x Blastoise-Holo (Pokemon Game 1999 - 1st Edition)
2x Chansey-Holo (Pokemon Game 1999 - 1st Edition)
3x Charizard-Holo (Pokemon Game 1999 - 1st Edition)
4x Clefairy-Holo (Pokemon Game 1999 - 1st Edition)
3x Gyarados-Holo (Pokemon Game 1999 - 1st Edition)
3x Hitmonchan-Holo (Pokemon Game 1999 - 1st Edition)
19x Machamp-Holo (Pokemon Game 1999 - 1st Edition)
3x Magneton-Holo (Pokemon Game 1999 - 1st Edition)
3x Mewtwo-Holo (Pokemon Game 1999 - 1st Edition)
4x Nidoking-Holo (Pokemon Game 1999 - 1st Edition)
5x Ninetales-Holo (Pokemon Game 1999 - 1st Edition)
1x Poliwrath-Holo (Pokemon Game 1999 - 1st Edition)
3x Raichu-Holo (Pokemon Game 1999 - 1st Edition)
3x Venusaur-Holo (Pokemon Game 1999 - 1st Edition)
4x Zapdos-Holo (Pokemon Game 1999 - 1st Edition)
1x Dragonair (Pokemon Game 1999 - 1st Edition)
1x Dugtrio (Pokemon Game 1999 - 1st Edition)
1x Electabuzz (Pokemon Game 1999 - 1st Edition)
2x Pidgeotto (Pokemon Game 1999 - 1st Edition)
1x Arcanine (Pokemon Game 1999 - 1st Edition)
2x Charmeleon (Pokemon Game 1999 - 1st Edition)
1x Dewgong (Pokemon Game 1999 - 1st Edition)
1x Dratini (Pokemon Game 1999 - 1st Edition)
1x Farfetch’d (Pokemon Game 1999 - 1st Edition)
1x Growlithe (Pokemon Game 1999 - 1st Edition)
1x Jynx (Pokemon Game 1999 - 1st Edition)
2x Kakuna (Pokemon Game 1999 - 1st Edition)
1x Machoke (Pokemon Game 1999 - 1st Edition)
1x Magmar (Pokemon Game 1999 - 1st Edition)
1x Poliwhirl (Pokemon Game 1999 - 1st Edition)
1x Seel (Pokemon Game 1999 - 1st Edition)
1x Wartortle (Pokemon Game 1999 - 1st Edition)
1x Bulbasaur (Pokemon Game 1999 - 1st Edition)
1x Caterpie (Pokemon Game 1999 - 1st Edition)
2x Charmander (Pokemon Game 1999 - 1st Edition)
1x Drowzee (Pokemon Game 1999 - 1st Edition)
2x Gastly (Pokemon Game 1999 - 1st Edition)
2x Machop (Pokemon Game 1999 - 1st Edition)
3x Magnemite (Pokemon Game 1999 - 1st Edition)
2x Metapod (Pokemon Game 1999 - 1st Edition)
1x Onix (Pokemon Game 1999 - 1st Edition)
2x Pidgey (Pokemon Game 1999 - 1st Edition)
21x Pikachu (Pokemon Game 1999 - 1st Edition)
3x Ponyta (Pokemon Game 1999 - 1st Edition)
1x Rattata (Pokemon Game 1999 - 1st Edition)
1x Sandshrew (Pokemon Game 1999 - 1st Edition)
1x Squirtle (Pokemon Game 1999 - 1st Edition)
1x Voltorb (Pokemon Game 1999 - 1st Edition)
4x Vulpix (Pokemon Game 1999 - 1st Edition)
1x Weedle (Pokemon Game 1999 - 1st Edition)
1x Clefairy Doll (Pokemon Game 1999 - 1st Edition)
1x Computer Search (Pokemon Game 1999 - 1st Edition)
1x Devolution Spray (Pokemon Game 1999 - 1st Edition)
1x Item Finder (Pokemon Game 1999 - 1st Edition)
1x Pokemon Breeder (Pokemon Game 1999 - 1st Edition)
1x Professor Oak (Pokemon Game 1999 - 1st Edition)
1x Water Energy (Pokemon Game 1999 - 1st Edition)
1x Alakazam-Holo (Pokemon Game 2000 - 1st Edition-Italian)
1x Charizard-Holo (Pokemon Game 2000 - 1st Edition-Italian)
3x Zapdos-Holo (Pokemon Game 2000 - 1st Edition-Italian)
We already knew which of those were PSA 10 (as per data above), so of those these were the ones with new PSA 9 additions:
1st Edition (PSA 9 changes)
2x Alakazam-Holo (Pokemon Game 1999 - 1st Edition)
1x Clefairy-Holo (Pokemon Game 1999 - 1st Edition)
5x Machamp-Holo (Pokemon Game 1999 - 1st Edition)
1x Nidoking-Holo (Pokemon Game 1999 - 1st Edition)
2x Ninetales-Holo (Pokemon Game 1999 - 1st Edition)
2x Zapdos-Holo (Pokemon Game 1999 - 1st Edition)
1x Arcanine (Pokemon Game 1999 - 1st Edition)
1x Charmeleon (Pokemon Game 1999 - 1st Edition)
1x Dewgong (Pokemon Game 1999 - 1st Edition)
1x Farfetch’d (Pokemon Game 1999 - 1st Edition)
1x Jynx (Pokemon Game 1999 - 1st Edition)
2x Kakuna (Pokemon Game 1999 - 1st Edition)
1x Magmar (Pokemon Game 1999 - 1st Edition)
1x Poliwhirl (Pokemon Game 1999 - 1st Edition)
1x Charmander (Pokemon Game 1999 - 1st Edition)
1x Drowzee (Pokemon Game 1999 - 1st Edition)
2x Gastly (Pokemon Game 1999 - 1st Edition)
1x Magnemite (Pokemon Game 1999 - 1st Edition)
2x Metapod (Pokemon Game 1999 - 1st Edition)
1x Pidgey (Pokemon Game 1999 - 1st Edition)
3x Ponyta (Pokemon Game 1999 - 1st Edition)
1x Squirtle (Pokemon Game 1999 - 1st Edition)
1x Voltorb (Pokemon Game 1999 - 1st Edition)
4x Vulpix (Pokemon Game 1999 - 1st Edition)
1x Weedle (Pokemon Game 1999 - 1st Edition)
1x Water Energy (Pokemon Game 1999 - 1st Edition)
1x Charizard-Holo (Pokemon Game 2000 - 1st Edition-Italian)
2x Zapdos-Holo (Pokemon Game 2000 - 1st Edition-Italian)
No cards in this timeframe received PSA 9 grades with a qualifier (e.g. 9(OC)) .
I wish I had data which went all the way back to 2018, but for now I’ve only started periodically polling the data since starting this thread just over 2 weeks ago.