Frank, you make a very good point and one I've thought a lot about in relation to many songs that are now attributed to a contemporary composer or songwriter but which take all or large parts of their tunes from songs written before 1920 (or perhaps never formally "written" by whoever wrote them in the first place.

[[I understand that the melody for Dorogoj Dlinnoju is a traditional song and might predate the copyright from the Soviet Union. I don't think it matters much whether you borrow the melody from another song and put your own lyrics to it.
You can claim authorship of the lyrics. Not sure what Gene Raskin did here, but the tune was floating around prior to copyright date. It's a Russian Gypsy tune.

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Every songwriter I know has taken the melody from some song or other and composed their own lyrics to it.   Woody, Dylan, McCartney, Harrison, ....plenty of pop songs based on PD tunes. I think in the realm of folk music, the tune is a vehicle for the words and is of less importance in its originality.

Now if someone were to claim authorship of a tune by Gershwin, Berlin, Porter, or Kern et. al. then that might be a little different. Many of those tunes were original and not PD.]]

I often see pop or show tunes or even folk tunes attributed as "words and music by [somebody from the late 20th C.]," when more than half the tune is borrowed from a classical composer (who probably borrowed the melody from a trad folk tune), etc.   Sometimes they do say "Based on a theme by ______," but not always.   I like to see the sources given due credit when the music composers are listed.