Well, in 1875 my great-great-great-grandfather shipped abort
of the Cutty Sark as an apprentice. Fascinated by the chantying,
as soon as he got ashore he ran into the gift shop and bought
himself a copy of Hugill.

But seriously, I believe the question is still answerable via
primary sources--- ask a Baroullie Whaler or a Menhadan Chanteyman
how the songs and the role of leading them came to him. I suspect
the answers would be much the same as those who sang in tall
ships.

Similarly, I believe the question is in fact best broadened to
one about work songs in general, particularly those used at
heavy labor by workers who are in large proportion illiterate.
How did members of chain gangs learn their work songs, then
transition from chorus to lead?

At the same time, it seems to me that the learning process in the
literate--- such as Harlow, Dana, etc., would be markedly different.
Affected, if you will, by the very literacy of the individual and
by their role as a chronicler of the events of which they were a
part. By the same token, a captain or wife writing an interesting
lyric down in the log wouldn't have gone through the same process
as the apprentice or AB using the work during his learning process.