A colleague asked about the public domain status of a short musical play that was written in 1959 in honor of a local event. The writers never intended to profit from the musical and in fact gave away recordings of the
musical.
I would do a two-part analysis in evaluating public domain status: (i) an analysis of the copyright status of the words/melody/lyrics/text/etc. that comprise the "book of the musical" and (ii) another analysis for any existing physical recording of the musical.
With respect to the "book of the musical", a 1959 work is governed by the old Copyright Act (the 1909 Act) which required filing of a renewal application after 28 years. If the creators of this musical wrote it "for fun" and gave copies of it away, it's quite possible that no one bothered to file a copyright renewal application. A work first published in 1959 for which no renewal application was filed is in the public domain.
Determining public domain status of any recording of the musical is where the query becomes really interesting. Sound recordings made prior to February 15, 1972 are not protected under federal copyright law. However, this does not necessarily mean you are free to use any pre-1972 sound recording in any way you please. Pre-1972 sound recordings can still be protected by state law and such state law protection can potentially be valid until 2067 (due to some very confusing pre-emption language in Section 301 of the current Copyright Act). Anyway, with respect to the “public domain” status of a pre-1972 recording, you have to figure out which state law applies and whether that state offers any protections for the recording that are still in effect.