Strange things can happen, though.
Besides my 69 RS coupe, the other car I have is a 66 Chevelle which has been in the family since it was first purchased on March 30,1966. I have all of the original documentation including protect-o-plate and have verified all of the numbers when the car was restored between 1995 and 2000. I even found a date code on the frame. Point is that everything is within a couple of weeks of the mid March 1966 build date at the Flint, MI assembly plant, except for the rear axle which is date coded Oct 1965. Axle date code, etc and POP totally agree. The rear end was build at the Buffalo Gear and Axle Plant and obviously set around somewhere before it made the trip to final assembly.