In 2015, Google introduced new candidate lists to include volumes beyond those determined to be public domain based on their publication date. These included selected volumes from the US Renewal Era (1923-1963), which may not have had a copyright registered or renewed, US Federal government publications, US state government documents (from states where such materials are public domain), and various international government documents. Google’s decision to include targeted volumes from the Renewal Era was an astute one: a 2019 study from the New York Public Library estimates that 75% of volumes published in the US Renewal Era may be public domain due to lack of registration and/or required renewal.