Posted by Steve B on Wed Dec 30 16:10:18 1998, in response to Re: Original IND Letter Designations, posted by Mellow One on Wed Dec 23 22:05:02 1998.
One other point: by the time the 6th Ave. subway opened in 1940, the 6th Ave. el had been dismantled. It ended service in December 1938, and demolition was completed in 1939.
There is a photo in Building the Independent Subway of a C train on the first day of service on the Concourse line. I'll have to check if the upper destination sign was set for 205th St. or Bedford Park.