I don't think it is O-1 steel, but is actually stainless steel that is unmarked.
I believe tenite was used from mid-1950’s to mid-1960’s. The “SS” stamp was not used until around 1963, and a year or so later the “SS” was changed to a single “S”. Before that time, there was no marking when stainless was used. Here are two of these earliest stainless markings.
-Steve