Wikidepedia addresses this just a bit
Earl Scruggs turned Soldier's Joy into Old Folks. Old Folks is one of the tunes that got me into playing the banjo.
To me, 'Injun Rubber Overcoat' appears to be an ancestor of Willie Dixon's 'Spoonful'.
And of course Love me Tender is Aura Lee. Jesus Loves the Little Children is Tramp, Tramp, Tramp the Boys are Marching. Battle Hymn of the Republic was John Brown's Body, and before that it was Say Brothers. Turkey in the Straw was Zip Coon which came from Natchez on the Hill. Melodies are constantly recycled.
Old Virginie Jig and Old Molly Hare?
I often compare old johnny boker to big bend gal by the shelor family