If there were three poems that came out in that 20 year period that our previous scholar knows of, that all had the same general context of death at sea, they might be still varied enough in content to have spawned these different songs, but still along the same lines as what I introduced above.

This is sort of the "lost wax" approach to tracking down a song--the suggestion that there is an as-of-now unidentified poem that was hanging around in the period from 1839 - 1859 that might have gone through this process. It's a long shot, but it might give someone a direction to follow.

SRS