Invaders don't count because they aren't a true generation. They skip the normal audition process because they were all known quantities up to that point and got brought in with identities that were either the old IP of another company (Lumi, Yuri, Ember) or reminiscent of their old Identities (Jelly and Dizzy). They're Vshojo esque adoption agency within Phase.Half a year still doesn't seem like a very long time for a new gen announcement. Though, maybe Phase Invaders didn't count.
Edit: Yeah, I'm gonna say that Invaders are probably their own thing. If that's the case, it makes a lot more sense.
Sorry for the double post.