Luanne Goodson, WorldCat Quality & Partner Content Department, has provided the following information concerning the importance of recording standard numbers, such as ISBNs, ISSNs, and UPC codes. December 2013.
Many standard numbers may be recorded in bibliographic records. They are also indexed and can be very useful for searching and retrieval. Most catalogers are aware that you can retrieve a bibliographic record in WorldCat using the International Standard Book Number (ISBN) as a search key. You can read about field 020 (where the ISBN is recorded in a bibliographic record) in Bibliographic Formats and Standards (BFAS) http://www.oclc.org/bibformats/en/0xx/020.html. You can read about retrieving WorldCat records via ISBNs on the Searching WorldCat Indexes page: http://www.oclc.org/support/services/worldcat/documentation/searching/searchworldcatindexes.en.html
Searching for accession numbers, such as the OCLC control number or LCCN; standard numbers, such as an ISBN or ISSN; or a class number, such as a Dewey or Library of Congress classification number, is one of the most efficient ways to search. So it is particularly important for catalogers to include such numbers whenever possible in the records they enter.
Another standard number, which may be more familiar to audiovisual catalogers, is the Universal Product Code (UPC). This number is recorded in bibliographic records in field 024 with first indicator coded '1'. Field 024 http://www.oclc.org/bibformats/en/0xx/024.html also allows for recording other standard numbers or codes which cannot be accommodated in another field (e.g. 020, 022, or 027, etc.)
Many standard numbers are specifically indexed in WorldCat. The index labels and searches for these numbers can be found on the Searching WorldCat Indexes page http://www.oclc.org/support/services/worldcat/documentation/searching/searchworldcatindexes.en.html by choosing "4 Search index check list" in the box on the upper left of the page.
By recording standard numbers in bibliographic records catalogers save time for everyone who searches WorldCat and assist other catalogers in finding records, which in turn cuts down on duplication of effort.
If you come across a WorldCat record which needs a number added, please feel free to add it. If you cannot add it yourself, please send a note to firstname.lastname@example.org requesting that the number be added. (Please note: OCLC QC staff process requests in the order they are received. Due to the extremely large numbers of requests, QC staff will only respond in special situations.)