if you shot peened it, would it be done before or after the carburize process? that might be it right there if different companies had different preferred methods
Shot peen for strength would be done after carburize. The carb temperature is too high to retain the mechanical benefits if shot peened before. Shot peen isn't always applied though, and may or may not remove the copper. I know the machines I worked with would strip that copper off in a heartbeat - which is why we wouldn't have put them in our equipment, the contamination would relegate that work station to use ONLY with parts that don't get any subsequent finishing operations (platings and the like).