I like to group all kinds of things by Group. While it appears to be an option with Custom Forms, it's not a true Group ownership. I've been using the Share function to grant Groups access to Custom Forms as applicable, which works at the surface. If a form, though, has no Group access assigned, the "Group" appears to default to some sort of association with the creator. If that creator moves Groups, the form doesn't follow. This makes it difficult to track who and how Custom Forms are managed.