This info is also posted somewhere else on AAPK, but I couldn't find it easily, so here is a duplicate.
KA-BAR Knives and dating them
1898-Tideoute Cutlery Co. formed in Tiedoute, PA
1902-Factory purchased by Wallace Brown, Started in Tideoute, PA as Union Razor Company
Union Razor Company, Tideoute mark used 1902-1909 (Equivalent in Case language--Case Brothers, W. R. Case &SON)
Union Cutlery Co. Tideoute marked knives were only made 1898-to approx. 1912. (Equivalent in Case language--Case Brothers, W. R. Case & Sons)
Union Cutlery Co. with North American outline 1912-1923 (Equivalent in Case language: W. R. Case & Sons, Case Bradford PA)
Union Cutlery Co. Olean, NY 1912 first used.
OLCUT, and Keenwell also used first in the 20's.
After 1923--KA-BAR on main blade, and Union Cutlery Co. Olean, NY on either the back of the blade if a single blade, or on one of the smaller blades. These will be referred the Union mark. If I state the Union mark it means the blade will be stamped "Union Cutlery Co. Olean, NY" (Equivalent in Case Language: Case Tested)
After 1952 Union Cutlery Co. is no longer marked on the knives. (Equivalent in Case Language: XX and USA)
Kabar, USA was changed to in 1951
In the 70's a pattern number was added between the Kabar and the USA. (Equivalent in Case language: Case dots)