Current production Winchester 101s are manufactured in Belgium with assembly in Portugal . These use a different mechanism and numbering system than the vintage Japanese-made versions.
A "K" prefix in the serial number usually indicates manufacture after 1967, often associated with the Kodensha plant.
The Winchester Model 101 12 gauge was manufactured after 1971, but no serialization records currently exist. 20 Gauge, 28 Gauge, & Midwest Gun Works
For models produced between 1972 and 1987, experts often estimate the date based on features. For example, the presence of Winchoke (interchangeable screw-in chokes) typically indicates production between 1981 and 1987.