Just curious, why would there be a month between when the car was built and when it was delivered??

Or do you mean ordered, then delivered?

Otherwise your theory could be right. I'd guess that it was something discovered at the plant, old stock shipped or mixed/dated inventory and then taken care of in the "repair" area at the end of the line after final inspection. A lot of that stuff goes on in an assembly plant. I have a 63 383 that is stamped coded as a "36", which is means it should be a 361!! Externally, they look the same. When stock gets low, stuff happens to keep the line running.