OCNs are particularly useful as identifiers for books and other bibliographic materials that do not have ISBNs (e.g., books published before 1970). OCNs are used as identifiers often in Wikipedia and Wikidata. In October 2013, it was reported that out of 29,673 instances of Book Infoboxes in Wikipedia, "there were 23,304 ISBNs and 15,226 OCNs", and regarding Wikidata: "of around 14 million Wikidata items, 28,741 were books.