This is such a lovely old song and haunting melody. I always thoughts the lyrics I knew were fragmented, and began to suspect it has undergone some serious 'evolution.' It does seem likely that into the modern American era its evolution, once latched onto the fixed images of Shenandoah, and more precisely Missouri (river) the evolution stopped, or slowed. And, in this modern format, its simple story makes sense - but I would love to have heard sung some of the very early versions ... especially the sea chanties which must have differed greatly, growing within the closed, limited horizns of a ship on a transoceanic voyage. It would be a treat to go back in time and collect several verions!
This has been a great, long lived thread!