Not to mention we, as humans, are incredibly good at distinguishing minor differences in faces. Just learning how to draw them in the first place was tough for me. So try not to get caught up in making it perfect and keep up the good work.
That being said, there are some tricks I use to help keep things looking solid, like irresponsiblepics said a 3D representation can be invaluable, lately I have been making concept art for the alien characters in my comic and I would often make a side profile that is really cool but struggle to draw it in a different perspective, especially head on. So I took the best pieces of art and put them in to blender (a free 3D modeling and CGI software) and made a crude 3D model of them. (plenty of tutorials on Youtube on how to this). This has three big benefits, one is that, if there is discrepancy between two or more views, you are forced to reconcile them, second, you now have reference for any angle or perspective, and lastly, FREE LIGHTING REFERENCE! 
One of the original profiles.

Modeling.

lighting example.


3D print of the final result and the head on profile I couldn't draw