Multiple ISBN on a single bibliographic record

Multiple ISBNs are acceptable on a single bibliographic record. Hardcopy items may have additional ISBNs for the paperback, online, and CD-ROM versions printed on the item, just to list a few possibilities. Library of Congress Rule Interpretations 1.8, 1.8B2, and related rules would have the cataloger record all ISBNs that appear on the resource, with the ISBN for the item being cataloged as the first 020, if that applies.  Any parenthetical identifier for any of the ISBNs should be included; the LCRI says:  "Prefer qualifiers found on the bibliographic resource itself when they are judged to convey a condition intelligibly. Use judgment to deal with unusual, complex situations or unusual phenomena." MARC 21 further stipulates that "Only the ISBN applicable to the entity represented by a particular record is considered valid on that record,"which means that all of the other ISBNs should be coded in field 020 subfields $z. OCLC #687665134 is one example of a record with more than one ISBN.

(Source: OCLC message of the day through OCLC Connexion)