Pseu
Not got a lot of time now - just thought I'd comment in passing
You may well regret opening the Pandora's box of definition - 'a lorra men did and a lorra men died'
The problem with Roud's, or anybody's re-definition depends on whether you can redefine something that is no longer alive
Can you re-define 'Elizabethan Madrigals' or 'Medieval Hymns' or 'Victorian Parlour Ballads'?
You can't, in my opinion.
You can certainly fill out existing definitions with information that has been missed, but this is not what the re-definers have done

I believe 'folk song' to be a specific term which defines who made them and continued to re-make them.
When Sharp and his colleges were operating, they believed that they were 'hearse-chasing', and to a degree, to a great degree they were correct.
New songs were not being made, the places for singing had largely disappeared and the dominance of broadsides meant that the songs were still-born (we have lots of examples of old singers who wouldn't dream of altering a printed text)
Eventually, the singers changed from being active participants in their culture to passive recipients of it

We were lucky to have worked in two major traditions.
The Irish Traveller song culture was very much alive when we started, open air and pub singing sessions were common and self-made songs were still being created
Within eighteen months of our starting, the singing tradition screeched to a halt when the Travellers got portable televisions and the singing and songmaking stopped
There's been a bit of a revival since, but that's what it is - a revival
While we missed the best, we did have the opportunity of working with people who had been part of a living tradition.

In the West of Ireland, the singing tradition all but died by the beginning of the 1950s, with the exception of the Gaeltachts.
till a lot of old singers and plenty of songs but not many venues.
Where Irish settled singers were remembering songs from a rich living tradition, the English singers were remembering songs which has been learned from forebears who were remembering them - second or third hand.
I don't believe you can re-define anything from those situations.

"Dirty Old Town"
MacColl denied that any of his songs were 'folk songs' - he made a point of doing so
He did believe that making new songs might eventually lead to the recreation of a tradition, but that never happened, a couple of his Traveller songs nearly got there, but the singing tradition died before they took root.

MacColl was a strong supporter of Lloyd's statement in the last chapter of his 'Folk Song in England':
"If 'Little Boxes' and 'The Red Flag' are folk songs. we need a new term to describe 'The Outlandish Knight'. Searching for Lambs' and 'The Coal-owner and the Pitman's Wife'."
So am I
Jim