As I have had to do many times with coins, I have needed to use a magnifying glass to determine the difference between an overstrike and a die or stamping error. Deep stamps can be confusing as we know with the "3" and "8" stamps on Krags. A small piece of metal in the die upon stamping can marr or alter a clean stamp as can damage to the die where there is wear or a piece broken which can cause a mis-strike.

Fascinating post with many potential variables.

I would love to see some more pictures that represent some of these variations. Some of them need more magnification to determine exactly what is being viewed, I believe.