>>57918230
>>57918308
They made good use of the stock art by editing the backgrounds to mesh with the subject's art style. The quality lessened when Sugimori's style changed in Gen 3, but some card managed to salvage it. By Gen 5, the stock art usage overall came off as extremely cheap. It also helped that the better ones were early in the game's lifespan when the amount of illustrators and the expectations for the artwork were far lower.
Pokémon Aaaah! has an article detailing the stock backgrounds used in the TCG: https://www.pokemonaaah.net/research/tcgbackground/

Pic related.
>Old Sugimori art on Gen 1 card vs new Sugimori art on Gen 4 card
>New Sugimori art, Gen 4 vs Gen 5
>Old Sugimori art, Gen 1 vs Gen 6 callback