"My copy of Travellers' Songs Of E & S clearly states "
The book is copyrighted because it was edited by Ewan and Peggy - all such works belong to their editor
The individual songs most certainly are not, which is what we are discussing - the new 'Penguin Book of English Folk Songs is copyrighted to Steve Roud and Julia Bishop
Hoot quoted an earlier book - I though I had all MacColl's publishes stuff - I'd love to add this one to the collection   
Another bit of MacColl necrophobia bites the dust, it would appear

"Financial incentive"
MacColl, Seeger and Parker were paid by the BBC for the work they did on the programme - not for the songs
"we never got LPs of the original singers rather than the EM version"
After two of the radio ballads, MacColl and Seeger dited two of teh best albums ever produced of field recordings - 'Now is the Time for Fishing' after 'Singing the Fishing' and 'The Elliots of Birtly' after 'The Big Hewer'
There was to be a third on The Stewarts of Blair after the Travelling People (we have the edited recordings), but Folkways never issued it.
The Radio ballad team made a verbal contract with all those recorded at the end of the interviews - again, we have the actuality
I have no idea whether the BBC or Folkways ever honoured those contracts - I assume they both did (though I do know from experience that the BBC only paid a pittance and most of the record companies weren't much better, if they paid at all)
It was never really about money in those days and with some of us, it still isn't
Do you have the title of that 1957 publication Hoot - my two, containing the two songs you mentioned, are dated 1953 and 1964 - not copywriter either side of your date ?
It's become a 'must get' (there is no evidence of it on either the MacColl site or in 'The Essential MacColl' lists of publications
A mystery indeed
As far as our own collecting goes, we credit the songs as being traditional but the versions attributed to them (not copyrighted)
Jim