After 1975, John Deere changed the way they did their model series (type codes) to include the model number, i.e. C210D meant it was a 210 and the last letter was the year, in this case "D" was 1975.
Here is the letter code for the year break down.
D=1975, E=1976, F=1977, G=1978, H=1979, J=1980, K=1981, and L=1982.
Starting with 1983, Deere model series number looked like this M00210X, which was for a 210 tractor made after 1982.
For pre-1975, the type codes were used and from that you could decipher not only the tractor model, but what tires it had, etc.
The following 3 files show the round fender 110/112 (1963 to 1967), the square fender 110/112 (1968 to 1974) and the 140 tractor.