Common parts like starters, alternators and all other components that were attached at the engine dress line for base engines were usually (not always, but usually) much closer to the build date of the car than parts for optional engines. For example, my 68 L78/L89 was assembled the 4th week of May, 1968 and the distributor is dated late March, 1968. The Holley carb is also dated late March, 1968, so you can see there's a big difference. Heck, the aluminum heads are dated late January, 1968!
Ed