The next thing to do here is perhaps examine the dodgy content in the song. It's obviously intended as a tongue-in-cheek piece. I know that because I write similar tongue-in-cheek pieces based round maritime themes (including whaling) myself. I have done a lot of research using historical documents, literature on the subject, and where available personal recollection (re trawling industry and inland waterways). I suspect Neil was coming from the same place. If you go back to the late 1960s this sort of thing was common and not an issue. Most performers were accepting Bert's refacimentos without question, and brilliant they were too. There wasn't as much pressure to declare how much of a song was your own invention. the boundaries were much more blurred. From a historian's point of view that is to be deplored, but it was what it was. Performance was much more in the ascendant as opposed to truth and scholarship.