Looking at the first two superimposed photos (SW 642 vs. Kahr PM-9 and SW 642 vs. SW BG 38), it looks like the 642 shrunk in height from about 4 and 7/8 inches to 4 and 1/2 inches. Maybe it was left in a pocket and got ran through the washer and shrunk.
Seriously, thanks for the graphics.
I've pocket carried a SW Model 38 and felt very comfortable with it. I now mostly carry a Kahr CM-9. After break-in, mine has been reliable. I like it because I can shoot it better than my other small, double action handguns.