"He *really* sounded authentic. How'd he do it?)"
Probably by collecting all those rags and bones!
Authenticity seems to be a movable feast.
For instance, the BBC recordings of shantyman Stanley Slade (without that awful BBC chorus), are in my opinion, far neared to that of MacColl and Lloyd's singing than they are to Hugill's. Different again are the recordings of R H Rassmussen and (?) Halliday
Authenticity is in the ear of the beholder maybe.
Jim Carroll