Either you or Jerry are a little mixed up. The slide stop NOTCH in the SLIDE was heat-treated along with the front end of the slide on the M1911A1 starting somewhere in the early '30s. We were beginning to fully treat slides as the war ended. Only a very few fully-hardened slides got on frames before production was halted in 1945. Colt continued with development of the fully-hardened slide and they began to appear on Government Models a few years after the war. You may have one of those slides on your Colt since Colt sold a number of them to the gov during the Korean war. Later, they bought fully-hardened slides from many contractors.