Misteltoe bough, Yesterday, Mull of Kintyre,Daisy daisy all started off as popular composed pieces,.
I see   a flaw inthe 1954 definition. Paul MacCartney wrote two of these, if Fred Jordan or any other traditional singer had sung these in their own style, they still would not be traditional songs, nor would Sweet thames flow softly [ewan maccoll] nor would the Mistletoe Bough[ Thomas Bayley1884].They are songs written in a traditional style, but not traditional songs.