It will always be a matter of opinion whether a change was an improvement or not.

Anyone who changes a song, even if he changes it unconsciously, will probably feel that his change is an improvement. Others may disagree.

A lot of good stuff seems to get lost. Clever wordplay is often lost. Anything that people don't understand tends to get changed to something they do understand—and think of the lowest common-denominator of understanding here. The result is often something less poetic or expressive than the original. Archaic expressions, unusual words, references to obsolete technology and customs, all tend to get replaced with something more modern.

Long songs tend to get shortened as whole verses are forgotten. Our ancestors had more patience than we do for listening to long ballads. Our abbreviated versions of ballads sometimes lose so much detail that they no longer make sense.

I have made quite a hobby of looking up old songs, and have often made it my goal to find the oldest known version of a song. When I succeed, I nearly always like the old version better than the current best-known version. But others often don't agree. When I'm responding to a request, I often find the requester saying, "No, that's not right." It often turns out that they want the Chad Mitchell Trio version, not the Georgia White version; or the Lonnie Donegan version, not the Leadbelly version; or (heaven help us) the Pat Boone version rather than the Fats Domino version. De gustibus non est disputandum.

People are afflicted with nostalgia—your first kiss, the first car you ever owned, your first guitar, the first computer you ever learned to use, and so on, will probably forever occupy a special place in your heart. Likewise, the first version of a folk song that you learned to love and sing will probably always seem like the "right" version, no matter how recently it was coined when you learned it.

Nowadays, the best-known and most-requested version of any song tends to come from somebody's recent hit record—and the last 40 years counts as recent in the history of many songs. So I'd say it's recording, not writing down, that tends to establish a certain version as definitive in the minds of many folk-music fans.