The copyright date of the piece (1983) is not necessarily the date of the sheet music publication - especially when that publication references Ken Burns's "The Civil War.'
There were reprints that referenced the TV series. There were a lot before that, and they were the ones I was talking about. You can just go on Abe or Ebay and buy one if you want. Hint, this was published a bit before Keira Knightley could feature on the cover: