A good discussion of the threshold of copyrightability in musical arrangements and adaptations is here.
Toadfrog is rolling two separate issues into one: (1) the common-law right of first publication, and (2) state anti-bootlegging laws that apply to sound recordings. U.S. law replaced (2) with a statutory copyright beginning sometime in 1972. For recordings made before the 1972 date when Federal copyright in sound recordings took effect, state laws may still apply. The date when these state law provisions for pre-whenever-it-was-in-1972 were finally to be preempted by federal copyright law was 2047 under the 1976 law, but this has been extended to 2067 by the Sonny Bono Copyright Term Extension Act, a.k.a. the Mickey Mouse Protection Act. For more information check Professor Karjala's harmonization chart, lines 16-18. Toadfrog is right that the state anti-bootlegging laws, like the federal copyright in a sound recording, applies only to the recording, not to the matter recorded.
Many non-U.S. recordings from before 1972 are now covered in the U.S. by federal copyright law under a 1995 law called the URAA, which implemented some features of the GATT. I don't think state law applies to these recordings anymore, though I'm not sure.
The common law right of first publication (type 1 above) was replaced in the 1976 act with a statutory term equal to that of a copyright. For unpublished works created before 1978 and never "published" according to the legal definition of the word (which may have nothing to do with whether it was ever actually published or not) these common-law rights expire beginning on January 1st, 2003 for never-published works of authors who died more than 70 years before then. If the works are legally "published" before then, they are covered by a copyright which lasts until 70 years (previously 50) after the death of the author or until January 1st, 2048 (previously 2028), whichever is later. (See Professor Karjala's harmonization chart, lines 19-20.
All this, of course, it not legal advice, does not establish a lawyer-client relationahip, I'm not even a lawyer, etc., etc.