Believe there have been date codes on pre-production cars as far back as July '63, which I believe were parts carried over from Falcons. I'm sure there is a wide scattering of parts from Fall of '63 with higher concentration in the December-February time frame. Guess it depends on when the car was made, if it was pre-production or not and also which part it was as there were variations in early parts as they were modified to fit/function properly.