Dick Miles:

There are all sorts of Roseville Fairs, one of which is an adaption by Dick GREENHAUS.
There's also a very funny parody by Les Barker.
In fact it's the only Les Barker thing I think is actually funny.
I suppose the thing to do would be to attribute the song 'Staines/whoever'.
But this ain't 'collecting'.

On another tack, what about poems which later research found to be of known authorship which were unearthed, tunes surreptitiously ascribed to them then given to revival musicians as newly discovered 'trad' pieces? Bert Lloyd was particularly adept at this stunt.