Gibb will no doubt give us chapter and verse, but the impression I get from reading around the subject is that chanteying gradually gained momentum from the 1830s possibly reaching a peak by the 1860s and declined from then onwards with the increase in steam power and increased mechanism. To me this means descriptions from people's memories upto c1900 would still be valid but after this their value would begin to decrease. Certainly by the 1930s I would be wondering how much any chanteys collected were influenced by what had already been published.

Jon makes the very strong point that many of the well-known chanteys have pretty standard texts that are well consistent, Hanging Johnny, Blow the Man Down, Rio, Whiskey, etc.