I have a 64 SS convertible. The assembly date is 12B and the body number is 2319. I interpret the assembly date to be the 2nd week of December. Was it assembled the second week of 1964 or 1963? As long as I can remember, the introduction of a new model years cars was always a little bit ahead of the calender year so it seems a little odd if they were building 1964 model year cars in December of 1964.

Your car was built Dec. 1963 My 69 was built in Nov. 1968

model years run (approx) from Aug 1963 to July 1964 (typical to this day).

Granted there are some exceptions to this, 1969 Camaro for instance but only at Norwood, Aug 68 Dec 69.