I know from experience that names and units somtimes got confused in the original records and also in the material compiled by the archivists who originally put together the Compiled Service Records in the National Archives. There was a John F. Johnson who served in the 48th Georgia. I wonder if there is anything in his CSR that might be related to John F. Johnson of the 48th Virginia? Perhaps a stray or unusual card reference that would have been out of place for the John F. Johnson serving in the 48th Ga.