"The earliest example I have of the use of St James found is 1918. We are not yet one hundred years from that date."

Sharp collected it from Victoria Donald on June 8, 1918, which makes it 99 years and 5 months. Mrs Donald was quite elderly, and it seems likely that she had not learned the song during the previous 7 months. Even if she had, whoever she had learned it from had had it in their own repertoire already.

"various versions close to the jazz one have been circulating the US. I have no problem in thinking that it got to Novia Scotia"

Except that the Nova Scotia version you kindly linked is nothing like the jazz version except in respect of the 'St James' line.

You've provided plenty of ideas and interesting information on this thread, but you seem to have developed a theory regarding 'St James' which you are now trying to bend the evidence around. Are you prepared to accept that the jazz song is a reworking of a pre-existing traditional song mentioning 'St James'?

If not, how did 'St James' get into an earlier Appalachian variant?

If so, why can you not accept that the Lenihan version might represent an independent example of the same strain of the song?