What I find interesting is how variations of well-documented contemporary tunes develop.

One example would be "No Man's Land" by Eric Bogle. The Furies learned it from the singing of someone who didn't sing Bogle's words to the letter. They recorded it as "Green Field's of France" and used the non-original (wrong!) lyrics. Due to the huge success of their recording it is now considered as the definitive lyric by many people who have never heard Bogle's version. This version has now, arguably, entered the tradition.

In a few hundred years will researchers be finding more variations and arguing about the 'original' or 'traditional' version.

With regards to the suggestion that 'traditional' = no known author. This is questionable as often the author is unknown simply through lack of research. Likewsie, if we consider people like Lonnie Donnegan we see a bigger problem. He used to credit works as 'trad' when the author was still alive, hence getting out of paying roayalties (intentionally or not).

The story of "The Lion Sleeps Tonight" is another illustration of 'invented tradition' where a recent composition was 'hijacked' and reconstructed under the notion it was traditional.

Bruno Latour makes interesting reading when he states that being modern is a very traditional thing.