When Malcolm Douglas talks about the collected versions of a particular song, it is important--you are just a folkie newbie, WAV, so it is just conversation--best thing for you to do is to listen to Ernie, Molly, and Merle sing "Dim Lights" about twenty times in a row--a lot to be learned there--

Which reminds me that in American taverns up until the time of prohibition, it was the custom for the gentlemen to informally gather and sing the old songs in improvised four part harmony--many of the songs sung in this fashion were collected in the volume, "My Pious Friends and Drunken Companions", and a number of those songs are among the body of songs typically regarded as "traditional"--

The harmony tradition was widespread much celebrated, and its passing was much lamented, Prohibition(1920-1933) surely killed it, but it had been fading away, even before then, for much the same reason that the old social singing customs were disappearing in the UK--

Even though the custom has died out, harmony singing still is regarded as having a special fraternal and familial quality about it:

Daddy sang bass (mama sang tenor)
Me and little brother would join right in there
Singin' seems to help a troubled soul
One of these days and it won't be long
I'll rejoin them in a song
I'm gonna join the family circle at the throne