Engine casting dates, especially at the beginning of production, can have VERY long lead times to actual build.
Case in point - my 1968 GTO convertible. This car is the
first ever produced 1968 GTO convertible, built at Pontiac Plant, body serial # 001, VIN ending in 044. This car was built on August 9, 1967, along with my one of my other 1968 GTOs,. which has VIN ending in 110. As luck would have it, there is another 1968 GTO convertible in town with VIN ending in 040 but has body serial # 004. It's nearly the identical car to this one (meridian turquoise). I talked with PHS regarding build sequence and they indicated that the earlier VIN of 040 car did not mean it was produced ahead of 044 for many reasons. This is especially true of very early production cars which were often pulled from line to have work done, then returned. These two were the very first two 1968 GTO convertibles ever built and they live within 20 miles of each other.
Engine cast date D247 (Monday, April 24, 1967), 107 days prior to production. EUN matches PHS. VIN stamp matches PHS. Due to the extremely early nature of this build, some of the parts were cast long before this car was assembled. I have a full breakdown of the build dates for car components available. Everything matches.