Beginning January 1, 2007, OCLC is going to implement the use of 13-digit ISBNs
Currently,monographic non-AV records may have both the 10 digit and 13 digit ISBN. If they do, and the bibliographical record is being edited, change the 024 first indicator 3 to a 020 with blank indicators. If by doing this editing, an exact duplicate tag is created, delete the duplicate tag. (10⁄25⁄06)
A 13 digit number usually appears on DVDs produced in Asian countries (e.g. China and Korea).
This is most likely an EAN. It belongs in field 024 with first indicator of '3'.
The 024 tag should not be used as a match point in merging records anymore. If a match point does not already exist in the target record, copy the 035 vendor-specific tag from the incoming record and paste it into the target record, save the target record, then import the incoming record. The incoming record will match on the 035 tag and allow you to select the option to merge. The other match points that are legitimate to use are the subfield a of the 010, and the subfield a of the 020 (Cataloging decision, 11⁄22⁄05)