There could be sheet metal dated within days, weeks or months before or after the scheduled build date. Most typically, the dates are within a few days, up to about 1-3 weeks. It is not unusual for a car to have missed the scheduled build date.
Inspecting all the sheet metal date stamps and date markings of individual components will give an idea of how close the car was made to the scheduled build date code on the warranty plate. Remember that a high degree of parts were dated... instrument clusters, heater boxes, heater motors, heater plenums, wiper motors, drive-train parts, wheels, etc...
BTW, I have an oddball car, a '68 convertible made on Dec 6th. As some know, there was a UAW strike in the Fall of '67. This car I'm restoring has August sheet metal dates and lots of late November sheet metal dates. Remember to consider what, if anything, was going on when a particular car was made... to try and make sense of oddities.