The engine and major component casting dates should pre-date the vehicle build date by anywhere from a few days to several months, depending on the assembly plant location.
If your car was built at Pontiac, the component casting dates could be very close to the vehicle build date, but a Fremont-built car should have more time (typically several weeks) between the component casting dates and the vehicle assembly date.
Also, be sure to consider the build date on your body tag, not just the invoice date on the PHS docs. Sometimes, the car could be built and spend several days or even a couple of weeks on hold or in repair area until it was released for billing/shipment.
1968 Pontiac GTO
1983 Pontiac Bonneville (G) wagon
2008 Pontiac G8 base