Well now, I just came upon Mudcat! My only claim to knowledgein this subject (sea songs & shanties), is that I once was a part of the performing group "The Press Gang", and, I was Captain of the 16th cent reproduction "Godspeed" on her voyage from England to the US (among other vessels).
Now, as to "lost chanties'; one evening at the Last Exit On Brooklyn, as I was in my cups, a friend who had been on stage recognized me in the audience. He called me up and requested a tune, so I responded. Afterward, a young lass came over to me and wanted to know where I had "got" those verses; she had never heard them before. The truth was, I made them up as I went along.
Cheers,
Geo
p.s. In my day, I would comment that sailor's voices had been ruined by rotgut whiskey and rotten tobacco, and I had spared no effort to achieve authenticity.
G