Well, your knife was made in the late 1960's in Ellenville, New York. The serial number was a warranty control number. It indicated how many of these were made before yours was. The pattern was first in the catalogs in 1967, production began late in the previous year.
Several stamping arrangements were used before they settled on the one that you are used to seeing, SCHRADE+/ U.S.A. 897UH
Also, the company owner changed the corporate status in late 1972 - early 1973 and renamed the company from Schrade Walden Cutlery Corporation, used since he acquired the Schrade company from the Schrade family in 1946, to Schrade Cutlery Corp.
The "+" replaces the stainless stamping in denoting stainless steel blades. That didn't come into use until some time in the mid to late 1970's. Schrade+ steel denoted two different varieties of stainless, 440a and 420hc (after circa 2000). Both supposedly received Schrade's own proprietary heat treat and quench (cryo too, I believe), and that made it "+".
Michael
