Checking my build date
From your user name I'm assuming you have a 76 Corvette, a trim tag date of C15 would be October 15th, 1975.
The letter represents the month of production. A was the first month, B the second, etc.. For most years, including the 1976 model year, production started in August - A on the trim tag. There were some exception years where production did not begin in August and A would represent a different month for those years.
John




