> the possibility that the composer had borrowed from a sailor song that was existing by the 1820s, or that some time after the 1820s sailors based a work song on a composer's popular air. Both seem plausible to me at this point.

If the "Three Little Indians" tune antedates Meineke's composition, it would increase the likelihood that the shanty already existed. If not, not.

It's probably impossible to show that the tune did *not* exist earlier.

The point is that there are two sources of evidence to suggest the shanty was in existence more than decade before Olmsted's voyage.

That isn't a very exciting claim, but it's about the best that can usually be made in 19th C. folk music research.