The way I understand it (in the US): you can copyright an arrangement. Even if the song is PD, you can take legal action against someone that copies your arrangement.

You can record any song as long as you pay the mechanical licensing fee.

However, you can't print or republish any recent folk songs that were first in print or copyrighted after 1923 with out getting permission. Then in 1023 it will change one year every year.

In order to challenge this you'd have to prove the song existed before 1923 or that the song existed before the copyright date (say it was 1932)- making the copyright invalid.

Does this seem accurate?

As for Dylan, he should have given the source of his text since it was exact (he did add one measure). And since Dylan did not copy the melody of the song- he has copyrighted an arrangement of "Love Henry."
Technically, he should have gotten permission from Arnold to use it.

Arnold did not pay anything as most collectors didn't to Hall for singing it. It seems unfair that she (or now her heirs) would not be eligible for compensation. The copyright by Arnold would be 1950- however, many of the songs were learned much earlier. The question of proving the date of the folk song arises.

Richie