Azizi, I am in full agreement with your views on this. Noting that all there is to go one is, as you say;
"That which can be observed is evidence, including first-hand sightings and written/oral statements. However, one must treat statements critically, as you point out. Most importantly, evidence must be taken in context, and that might be what determines "credibility."'
And I would also say that expolring "all" possibilities is in keeping with having an open mind & a better view, thus having a better "feel".
As far as the mishearing, misinterpretation, ajusting of words, phrases or meaning of lines in songs was a natural occurance (both by accident & on purpose, just as in the evolution in sailor's langauge) with the sailors & singers of shanties, "espically between 'white', 'black', 'southern costal', 'northern deep water', 'whaler' & 'flying fish sailor'. The culture of the seafarer was made up from the culture of the melting pot & their had to be cross pollination happening at every turn. It's nice to be able to put a finger on when this actually happens but becasue it's not 'documented doesn't mean it didn't take place, though that leaves us to speculate about the possibilities. IMHO, Hugill did much of this but statemnting where he seems to believe the orgins of many of his undocumented songs originated. But who better to speculte than himself. Well, when Roger Abrahams comes up with a new collection from a area that might be considered to be a new sub group of shanties, is there not some who'd be knowledgable enough to do the same as Stan and add their theories (I say onlt a theory)? I don't go about saying 'no' but would rather say it's a possibility & if it's a matter of a different 'splices' on the same line, so be it.

Barry