'NCC' is a registry prefix not an abbreviation.
A second letter indicating the aircraft's airworthiness category followed the N and preceded the identification numbers. These airworthiness indicators were; "C" for standard, "R" for restricted, "X" for experimental, and later an "L" for limited, (for example, NC1234).See FAA guide
Jeffries (the creator) was mistaken about the letter "C" being for "commercial" planes.
The last "C" seems to have been added by Jeffries for mostly aesthetic reasons with a. MA Wiki