I downvoted the first answer, because it was in error. I did not choose my own answer, another moderator did, likely because my answer was correct. And it did indeed answer your question. The reason you have a Grass Koffing and a Psychic Gulpin is because of the change in type between sets for the Poison type Pokemon. It is neither an error, misprint, nor bad card logic. It was a decision to strengthen the identity of each type and make them more coherent.