You may be correct about the poor stamping job. Looking very closely at the cylinder I can see how it's possible that the lines may have just overlapped a bit.
Thanks!
I looked at 2 different 657-2's last weekend at a gun show by 2 different dealers. Each one had an X plainly stamped on the cylinder. They were reasonably priced but I passed on them because neither dealer (or myself) knew what the X meant. Both dealers are a reasonable drive from my home. I hope someone can answer our question about the X factor here. lol