> ... what is involved in finding out about copyright limits, etc.

You will find information in US government documents if you do a
search on "copyright".  Basically, it lasts 70 years after the death
of the owner or originator, but there are provisos for works that have
been written but not yet published, and other clauses.  Music has some
additional provisos as well.  Unfortunately I've lost my reference and
am going by memory but it should be easy to find on the net.

In Australia copyright lasts only 50 years after the death of the
copyright holder.

Regards,
Colin MacKinnon