Looking back at these, it sure seems like his underbite becomes more apparent in each image. Some people have the tendency to exaggerate characteristics, others play them down. My natural inclination is to underplay them, which on the one hand is good for avoiding a caricature, but on the other, I can miss a likeness. Whatever you are more inclined to do, you can counterbalance it if you can recognize it. This applies to most every innate quality we all have as draftsmen. Look at what you tend to do in every drawing, and try and be objective about it. You can then both use it to your advantage when necessary and avoid it when it is a disadvantage. This photograph was taken not long after the last one, so not too many changes were made other than in the lower jaw and mouth area.