In 1999, as many books, movies, and songs were set to enter the public domain in the United States, the copyright term for works published from 1923 to 1977 was extended by twenty years. Two decades later, on January 1st, 2019, many works published in 1923 entered the public domain, making them available for use and adaptation.
Get the full story here: Guevara, Milton. “Freed from Copyright, These Classic Works Are Yours To Adapt”, National Public Radio, January 5 2019, https://www.npr.org/2019/01/05/682314361/freed-from-copyright-these-classic-works-are-yours-to-adapt.