I have 2 left showing...

Latent Ability iV (zone)
Potent Combo IV (rage/hunter)

The Achievement reads 189/200

So I was assuming there were 9 left I can't see.. more popping up after I complete Potent IV and more after Latent IV.

Based on your numbers, there must be at least 2 more pop up after I complete Potent IV.

How many more appear after completing the Portent IV mission?

I also think some are well timed to extend the missions overall. Easier missions appearing after harder ones are completed. I know when I completed the one requiring Quake, 4 or 5 more appeared, all relatively easier than that one.