If the serial number tag is missing you can estimate the year by when the castings were made. The bigger castings such as transmission, rearend, clutch housings, rear wheel castings, front support casting, etc will have a raised letter barcode.
Example: 12-31-‘S’ = 1950 year Barcodes started with A = 1931, B = 1932 etc. in alphabetical order to Z = 1954 (The letter V was left out on purpose) 1955 then started with ‘A’ again thru 1958 = D after that many letters were dropped from the system making it difficult to verify the year.