I finally found out this from a book dealer.
1909- Author listed as "Hampton Institute and Fenner." This continued with reprints through 1924. In introduction: "Arranged in 1909 by the Musical Directors of the Hampton Normal and Agricultural Institute from the original edition by Thomas P. Fenner."
Dett was not credited with editorial authorship until his 1927 edition.
Nothing was found on the 1891 edition with preface by Ludlow.
Unless there is a note with "Go Tell It On the Mountain" in the 1909 edition, it's presence should be credited to Musical Directors of the Hampton Institute, not Fenner.
I think this helps a little, but there are other credits to Fenner or Dett that should be to the Musical Directors.