I don't know about that.
So far the only aliens that haven't been fully confirmed to be appearing are Ghostfreak, Spitter, Buzzshock and Benwolf. We don't know if those four are in the first 40, or the twelve after that.
The only ones that have been explicitly stated to not appear in the first 52 episodes are Fasttrack and Jet Ray.
We don't know about ChamAlien.
That's just seven aliens. If they really wanted to, they could do one alien an episode for the remainder of the series. I really hope they do, if they haven't already. If they don't, well, I'll be severely pissed off. If OV misses out on being the series with ALLL the aliens just because of two or three guys I will flip a table.
Also CN needs to order like 40 more episodes.
Not that I think they will.
OV is already going to be the longest Ben 10 series to date. I wouldn't bet on them ordering more episodes, and that makes me sad.