Gibb, I wanted to respond to your perceptive comments. I think that the distinction you make between performance and historical texts (my words) with regard to shanties is very important. As you say, one probably doesn't get very far just trying to perform historical texts! I think the performance of a shanty today is in a way the handing on of a live tradition, if not of the actual working situation, at least of the singing of the song. This takes a lively shantyman with a quick imagination. One doesn't have to remember all of the verses in historical order, much less perform them!
On the other hand to try to establish the historical datability of certain texts and and to understand what they tell us about their own times is something else, and also well worth the effort.