Frank, I love your expression "popular songs of bygone times". I don't think I've seen a better definition for what most of us are singing. Of course if you extend the term "bygone times" further back into the past then you'd include "traditional folk music". (Also, I think that, if a song is no longer in some commercial chart or other, then it is also "bygone". But I'm not going to lose any sleep over it.)

You also say...The song "I Will Twine Mids't The Ringlets" was a composed song in the 1800's ....until it became Wildwood Flower in the folk tradition.
Could we also say that "British Workman's Grave" went through the same process when it was taken up and made fairly popular by a certain Irish group? Maybe it isn't folk but I think it falls under your "popular songs of bygone times" label.

Alice Flynn, "a scruffy mongrel" another good desription for songs that have changed and are changing.

Bert.