I think if any Xacto catalogues are found during the WWII era or pre WWII we may find some interesting facts about early Xacto tools.
The earliest we have so far is 1949, but we know the company existed prior to the war.
One fact we know is that the one-piece "Big Honker" #6 knife handles are pre 1949.
The two-piece handles are present in the 1949 catalog.
Interestingly, there are two versions of the two-piece #6 handle; the "early, Big Honker" hex grip, and the later, modern, smaller current hex grip. When the change occurred to this version I don't know, but it appears pre-1969.
I have all three versions of the "Big Honker" #6, and at least 4 of the modern #6.

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ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !