The problem with copyright is that it's a great big "He said, she said' game from hell.

For material in the PD, the lyrics may be 100% public - but by writing a new (or even just mostly new) arrangement, you then have the right to copyright the arrangement. This is where it gets sticky - as noted, HFA and other hounds of heck don't normally bother to sort out what's PD, and what's not. It's much easier and more profitable to threaten everyone and get money from scared musicians who can't afford counsel whether HFA's entitled to payment or not.

M