It is to make it clear for everybody. C is just the shortcut of Corvette (maneuverable warship called a corvette). Also known as the Vette. At least here in Europe. It is the same with the C63. Everybody know it means Mercedes AMG C-class or the e39 M5, for the BMW 5 series build from 1995-2001. whereas the E39 is the internal name from BMW for the 5 series.
The same apply for the C1-C7 it is the internal / officially Name for the Vette and Gen the name for the Camaro (Gemaro)
