Survival Knife Dating

[sideways22]

I have noticed that there is a month and year stamped on the tang nut on some of the Military Survival Knife and some do not have a date. Can someone answer why? Also, how long has Camillus coated the knives with black phosphorus? Thanks!

 

[CAMCO]

Camillus has been making the Pilot Survival knife since the late 1950's. The early models featured a 6" blade and the stamping was on the blade. In 1962 the government specifications were changed to a 5" blade. Beginning in 1967 the stampings were moved to the butt and now also included the month and year of manufacture. All Pilot Survival knives have a black parkerized blade.
Tom Williams
Camillus Cutlery Co.