What you say is true, Lighter. I simply take a more strict approach to reading the evidence in that I require some indication that a song was used as a shanty. Dating a song is one thing; dating its use as a shanty is another. The 1830s-ish existence of minstrel song "Coal Black Rose," for instance, which at some point was adapted to be a work song, does not suggest to me (n itself) that that sort of song had a life as a shanty in earlier days.

Steve, the info on "Chariot" suggests circa 1880s genesis of its shanty use. FWIW I group Chariot and DS in my mind (for right or wrong) due to their formal similarity to each other and their distinct difference from other songs that, and the end of it all, are grouped as "shanties." I can picture "Chariot" being developed as a shanty through the use of DS as a model. Just a thought.

The history of these two tunes is interesting, but at the same time (again a reflection of my personal disposition) I view them both as sort of "outliers" of the shanty phenomenon/genre. One is "too early," they other is too late!

"John Brown's Body" is a similar sort of song, I think, formally speaking.

Definitely shades of bagpipe tunes, I think, but I wouldn't limit it to that. The tune style could possibly be generalized to British Isles / Ireland music (?)