Utility Patent number 2,391,732 for the improved safety can opener was applied for on November 7th, 1944 and issued on December 25th, 1945. Normally a patent must be filed within one year of first use. So the actual design may have been produced as early as late 1943.
HOWEVER... (and this is where it gets interesting), the patent was applied for by it's inventor, Michael Mirando. He was a principal owner of Imperial Knives Associated Companies.
IKAC, at that time, included Imperial Knife Company, Inc. and Ulster Knife Company, Inc. Since they were the holders of the new Mirando patent, Camillus could not have used it without purchasing licensing rights.
Now, though the war had just about ended, a hot but quiet feud between Albert Baer (Ulster owner and partner of the Mirandos) and the Kastor brothers begun in 1939 had not ended. It is my opinion that the earliest Camillus (A. Kastor & Sons) might have obtained licensing to the Mirando patent would have been circa 1948, if not a few years later. The improved opener does appear in my copy of the 1951 Camillus Cutlery Company catalog.
John Goins Encyclopedia of Cutlery Markings dates the stamp you described to 1946-1956. As Tom Williams has told me often, take this with a grain of salt. Camillus was known to use older stamped blades after new ones had been introduced.
So there is the approximate earliest your knife might have been made assuming that the opener blade and master blade are both original to the knife.
Codger
