Terry, it's important to understand that from Continental's standpoint there were no 1957 Continentals. There were just Continentals that's why all the serial numbers start with C56.
The 1957 designation came about because of a dealer lawsuit which required Continental to differentiate between 56's and 57's.
What we call 57's was the result of product upgrading, cost controls, & re-engineering that Continental did and not a new model. The features all didn't occur at the same time (modified frame, engine upgrade, new colors, vinyl/leather interior, different rearview mirror glass, different hood, etc.)
Pat Marshall
Lancaster, OH