[Verne_Frantz]

Greg,

My research falls 6 years short of when your car was built, but based on many, many cowl tags from Baltimore from earlier cars, I believe these "extra" numbers refer to the body buck # (or "jig") that was used to build the body.
In 1964 Fisher Body at Baltimore built full size cars. They used 32 different bucks to hold the various metal pieces in place for welding, such as cowl, "A" piller, floor pan, rockers, quarters, roof, etc. Based on their expected sales of each body style, ie: 2dr Sedan, 4dr hardtop, sport coupe, convertible, etc, they had one or more bucks set for the right pieces to build those bodies. Each set of 32 bucks was called a "gate" (a gate of 32 cars). Other plants may have had 25 car gates or 20 car gates. By looking at my data on many of these cars, comparing these numbers to the various body styles produced, I've concluded these numbers correspond to the number of the body jig used to build "that" particular body. It would make sense that they would want to be able to document which body jig was used, in case some cars started to have problems later in assembly with things like glass or door fit, etc. The build sheets don't contain that information, and once the gate of 32 bodies was completed, they were banked until they were needed to meet the corresponding chassis on the Chevrolet side of the wall.
It does not surprise me that your pilot car is stamped with a "1".........
After all, pilot cars were built ahead of production launch to test tooling fit and establish assembly methods for the new models.

Verne
Again, I can not speak with certainty about the practices in '70.