If a song was written yesterday it would not have had time to be distributed enough to be accepted as folk

There is an anecdote in one of the Opies' books on children's songs about a little ditty from the abdication of Edward VIII.

Hark the herald angels sing
Wallis Simpson's stole our King

It was first spotted in London a few days after the abdication. Without ever having any media exposure, it got to Barra in the Western Isles of Scotland within three weeks.