Amos - you forgot to mention that it also refers to the inability of songwriters to remember the words of the songs they have written, or their inclination to just change the words after a while because they feel like it.

On the other hand, I was in the audience for an interview with Tim Laycock at Whitby Festival last year, in which he recounted how singers in Suffolk had for 200 years orally passed on broadside ballads without changing the words at all!

I guess "real" folksingers do remember, but revivalists adapt....

Depends whether you treasure the song as an historic artefact or to be sung for the enjoyment of the singer (or even, audience).