Publication in 1899 would prove it didn't originate in World War I, but not that it didn't originate in the Civil War.

Of course it's possible that the song was created ex nihilo by Davis in 1899, but there's some reason to doubt that (this post, as well as the Spottswood's liner notes, above), and let's not forget all the songs that A.P. Carter altered a little and then claimed to have written.