Well Artful, you could argue equally forcefully that it would be easy to compose a song (on a given subject, mind you) at one hour's notice if you were damned good at it. Harry Clifton used to make songs up on stage.

Incidentally, JBG had a close affinity with the local miners of Bolton - his music hall used to put on a Tuesday matinee especially for them.

Having looked into JBG's musical output, it's clear that many of his songs were in circulation for some time, in some cases years, before they were 'released' as sheet music.

That JBG's own work was plagiarised is evidenced by eg:

"NOTICE. Having printed numerous copies of J.B.Geoghegan's song 'Carried her to Belle Vue Jail' without his permission, I hereby make this apology, and agree to give him Two Pounds in consideration that he takes no further proceedings.

(Signed) J.H.Millburn, Comic Vocalist. September 21st, 1865"

JBG may well have adapted existing songs - but I have as yet found no evidence of it.