First, look at the tang marking. Schrade Walden became simply Schrade in 1973. At some point (1971-72 is an educated guess), they moved the marks from blade left to blade right. Shortly thereafter, they discontinued the serial numbers. The serials never were intended for dating the knives. They were placed there for warranty control. As production increased, and the numbers climbed, they gave it up. Production of the pattern as a regular item ended in 1991. It was used in small quantities later for special factory orders and even for one of the ill-fated 100th anniversary editions.