When we wanted to include "Mingulay" in the Rise Again Songbook, I looked long and hard to find out who held the copyright. I did find one printed version that had a copyright from some company - I can't be certain, but I think it was Curwen. Since our publisher, Hal Leonard, controlled rights to Curwen in the US, they let us print the song - but it was a little "iffy."
-Joe-