Posted by Ed Alfonsin on Thu Dec 24 10:28:02 1998, in response to Original IND Letter Designations, posted by Bob A. on Wed Dec 23 18:15:58 1998.
'G' and 'H' weren't part of the original IND lettering. One you left out is 'S,' 'Special,' used for the World's Fair in 1939-40 and later for various services (I rode a Yankee Stadium to 34th St-6th Avenue 'S' train in the 1950s, for example).