Simply to fine-tune the discussion, it appears to me that some chanteys are far more likely than others to stick to a standard development (and sometimes even standard words).

I'm thinking, of course, of Ranzo, Boney, Blow the Man Down, milkmaid versions of Rio Grande, and perhaps a few others. The impression comes from jotting down framentary chanteys given in 19th and early 20th century newspaper and magazine stories that are just different enough from the book versions to suggest independent collection.

This isn't to dispute the improvisational nature of much (or most) chantey singing. It's to suggest that some singers were more likely than others to memorize texts (and "floating stanzas") and repeat them more or less verbatim.

Anyway, I think that's what we should suspect, given the thousands of chanteymen of varying skill and disposition, along with a natural tendency to repeat a good song.