It's okay to overlap your references to spot mistakes, but I would review the work before overlapping them to see if you can see the differences. In time, you will spot the issues before overlapping.
As for reinforcing the corrections, do more life drawing studies and really take the time to work through what you are drawing. I would also encourage doing full shading on things as well, as that helps in understanding three dimensional form. When I'm doing something complicated (not just art), I find it helpful to verbalize what I'm doing, kind of like if I were making a tutorial for someone else. Might even be a helpful tool to record the session for yourself to see and hear everything so you can evaluate everything - this is kind of like what professional athletes do when they rewatch footage of themselves.
Art progression is iterative. Sometimes we have to revisit something multiple times, but I find it necessary to bring in something new and different to begin learning that, just so I don't get burnt out on trying to master noses. But in the process of studying the other things, I try to loop back in the previous subjects - knowing that they won't be perfect. Further down the line I'd revisit everything anyway, so like any piece of art, I'd be block in the larger shapes so that eventually when I draw stuff it will be better.
I hope that helps. I'm starting to come down with something and my head feels like it is full of cotton... ugh
