For anyone who has the same problem in the future, I did have to create new products (and subscription groups).

Gotcha that all makes sense! I'm currently trying to create the new subscription group, but I can't seem to figure out how to move the legacy products over to this new group. Is there a way I can do this? If not, do you know how I can proceed without cancelling the subscriptions of existing legacy users and moving them over to the new products (if I have to create new ones)?