Texture Atlas

Hello, I want to know about the texture atlas, as far as I know Minecraft's texture atlas has a limit of 16384x16384, you would get a crash indicating the texture atlas size limit has been passed when you added to many items textures of course, but is there a way to add custom models wich textures are not included in the texture atlas, for example, I was playing Cobblemon with a resourcepack that changes the missing mob models to sprites, so i edited one of those sprites in the resource pack to be 20k x 20k pixels, and it didn't give me any troubles, does anyone know why could that be?  And how to achieve this? The reason why Im asking this is to make some kind of resourcepack/datapack that adds tcg cards to the game and there are a lot of cards that have no less than 256x256 textures for the card art