New update:
I had been working on this since the last update, kept thinking it was getting better, but I looked at a previous version, realized I had gone too far in the wrong direction. So I basically threw out almost a month of work. But I think it was for the best. Not sure I'm there yet, or if I'll ever be totally satisfied, but as I've mentioned before, it helps my progress to update on the RPF.
I adjusted the lighting a bit again, adding some illumination to both sides of the face to help me to better see what's going on. One thing I realized was that the right side eye looked too high up. I realized I had been going back to one of the reference pics, adjusting just the eyes, but it wasn't lined up quite right, so my adjustments were off, with the right-side eye ending up too high. I needed to rotate the reference pic more. It wouldn't have really mattered if I had just adjusted the entire face to that image, but I was only working on the eyes, so it ended up wonky.
I've also realized that each of my cameras' focal length settings varied between angles, which can distort things - I had a lot of cameras with lower focal lengths which makes the face look thinner. So when I switched cameras after making adjustments based on one angle's focal length, things wouldn't look right from a different camera with a different focal length. I also didn't realize that when I use the "align active camera to view" function, the camera copies the viewport position but not other camera settings like the focal length or the other "lens" settings.
Anyway, looking at my updated pics right now, I see a couple things I want to change (right side needs a couple areas smoothed out, left side ear may be too big, etc), but I think it's better than the previous update. Hopefully I'll still think that later. I really want to be done with this so I can devote more time to other projects. I also want to put this up for sale if/when it's good enough.