also didn't karkat say he didn't remember which group he created first in the lab?? so they have no way of knowing which group would be the ectobiological "ancestors" and which would be the "descendants"

On this page Doc Scratch states that Meenah’s group were “to become the ancestors of the twelve they formerly regarded as theirs, and this twelve would be chosen for glory.” This is what happened with the Beta kids when they scratched as well. The descendants played but didn’t succeed so they scratched and their “parents” took their place as the players in the new session. So Meenah’s group are the descendants of Karkat’s group and Karkat and his friends are paradox clones.