just seen this thread, hope the following notes are of interest to some. I live in a village just outside Holmfirth and recount these from personal memory;
1. I used to hear this song sung regularly in the Stanhope Arms at Dunford Bridge, especially at shepherds and hun meets. One of the best singers was Tony Hirst, wo claimed to be a distant relative of Perkins but who was definitely married to Arthur Howard's grand-daughter. I'm sure Tony sang of "swains" and "lambs". He was often accompanied by his mother-in-law (Arthur's daughter-in-law) who is no mean performer on the squeeze box herself. She still runs "Rocky's Western Riding Adventures" at Dunford. Alas the Stanhope is no more, transformed into a trendy restarount it failed, closed and is now used as a sort of student actor's doss house.
2. the contorted vowel in pratty doesn't seem to occur in any other similar dialect pronounciation around here, but other vowels are usd in a very idiosyncratic way e.g. "love" becaims "lovv" (compare to Kate Rushby's very Barnsley "luv", "cow" becomes "coo" and "calf" caulf" (as in Gossip John). Holmfirth dialect and accent of the past could easilly have distorted pretty to pratty.
3. the pub called "Pratty Flowers" at Crow Edge wasn't so named until the late 1980's when new owners gave it a make over. prior to this it was known as "Prince of Wales", the landlord for many years was Geoff Hallas, a noted local climber.