It's more complex in the case of some works, as I've banged into before, regarding the old renewal laws. It seems that there is LARGE number of works (mostly from the pulp era) that fell out of copyright for a few years and then were renewed ANYWAY despite the fact that they fell out of copyright for 2 years.
This led to some wonderful confusion and lawsuits... mostly with Conde Naste in the center of it (the bought up a number of old Pulp Publishing houses back in the day and were the ones that renewed copyrights after that 2 year gap).
Walter B. Gibson, author of 90% of the Shadow novels ended up in a legal battle with them in his waning years over it, which ended when he passed away, as work he had written 'for hire' was included in that 2 year gap. He republished some of them as paperback books, and then Conde claimed they owned them. Since he died before there was any court decisions, there is no firm legal precedent but Conde Naste lawyers pretty much send out cease and desist and shut folks down who have shared this material through the power of money.
There's also a huge muddled mess on recordings of old time radio shows from prior to the changes in the 1970s law that included audio broadcast performances, which previously were not covered under copyright law. This is still argued over today in the courts with no definitive legal precedent decisions over old time radio collector hobbyists who preserved old recordings from the era of radio (transcription discs, wire recordings, etc.) and were trading and then later in some cases selling or internet distributing copies.
American Copyright Law is a mess, and regularly is meddled with badly. Generally whoever has the biggest bankroll wins in the courts, even when they are wrong.