Creative works may not have intellectual property protections for a number of reasons. In most cases, the rights have expired or have been forfeited. Basically, no one holds the exclusive rights to these works, meaning that living artists today can sample and build off those works legally without asking anyone’s permission to do so.

That’s why the New York Public Library (NYPL) has been reviewing the U.S. Copyright Office’s official registration and renewals records for creative works whose copyrights haven’t been renewed, and have thus been overlooked as part of the public domain.

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.