"Up to 75 percent of books published before 1964 may now be in the public domain, according to researchers at the New York Public Library."
The books in question were published between 1923 and 1964, before changes to U.S. copyright law removed the requirement for rights holders to renew their copyrights. According to Greg Cram, associate general counsel and director of information policy at NYPL, an initial overview of books published in that period shows that around 65 to 75 percent of rights holders opted not to renew their copyrights.
