Home → Cataloging in NC Cardinal → Appendices → Appendix F: 020$z Versus 020$a
Last Updated 04/02/2025
Determining when an ISBN should be in a subfield $z in the =020 MARC field rather than a subfield $a can be an important step in preventing the accidental matching and merging of records that should remain separate, such as when importing records with the Z39.50 interface or using the MARC Batch Import functionality. For example, a record for a single book should not be matched and merged with a record for a kit, even if that kit includes the book in question as one of its component pieces. The subfield $z helps to prevent this matching and merging, but you are still able to perform a search for an ISBN in a subfield $z in the catalog and Z39.50 interface, so you do not lose any important search functionality if the ISBN is in a subfield $z.
The subfield $z is typically used for cancelled or invalid ISBNs, but below you will find specific use cases catalogers should follow when cataloging certain items or materials.
As explained previously in the Knowledge Book here, when cataloging a kit, ISBNs for the included materials should NOT be listed in the =020$a, but instead in the =020$z. This, as noted above, will prevent mis-matching with Z39.50 and batch bib imports.
Occasionally you may come across a book that shares the same ISBN with another, entirely different and separate book. Some publishers will "recycle" ISBNs (this is common with small organizations, self-publications, and print-on-demand/public domain publishes). In such instances, catalogers should place the ISBN for the item in hand in the =020$z if there is already an existing record for a non-matching resource with the same ISBN in NC Cardinal and the records should not be merged. This has been previously noted in the Knowledge Book here.
Audio-enabled books such as VOX Books and Wonderbooks often share the same ISBN with the standard versions of their respective books, because the audio device is simply attached to an existing printed copy of the book with no changes made to the actual book itself. As a result, the ISBN will remain the same for both versions of the book. In such situations it is recommended that the ISBN for the audio-enabled book be listed in the =020$z, with the ISBN for the original, standard version of the book remaining in the =020$a of its corresponding record. This will help prevent the records for the different versions from being matched and merged. This has been previously discussed in the Knowledge Book here.
An example for this use case would be an encyclopedia.
Say you have an encyclopedia set that has its own ISBN, and each individual volume in the set has its own separate ISBN. You have included every volume in a single bib record.
In such an example, catalogers should include the ISBN for the set in a subfield $a, and the ISBNs for the individual volumes in subfield $z's, like below (including a subfield $q as demonstrated is helpful to let catalogers know which ISBN is for which item):
=020 \\$a9781414487366$q(set)
=020 \\$a1414487363$q(set)
=020 \\$z9781414487373$q(Vol. 1)
=020 \\$z1414487371$q(Vol. 1)
=020 \\$z9781414487380$q(Vol. 2)
=020 \\$z141448738X$q(Vol. 2)
Alternatively, suppose you only have one volume of a multivolume set. Or you want to catalog each individual volume as its own separate record. Then you would put the ISBN for the individual volume in a subfield $a, and the ISBN for the complete set in subfield $z (and again, including a subfield $q helps to denote which ISBN goes to which item):
=020 \\$a9780028974316$q(Vol. 1)
=020 \\$a002897431X$q(Vol. 1)
=020 \\$z9780028974392$q(set)
=020 \\$z0028974395$q(set)
Videos typically do not have ISBNs, and thus will rarely have a =020 MARC field, but the principle is the same for their UPCs, which are listed in the =024 MARC field, hence their inclusion here. This has been previously outlined in the Knowledge Book here.
If a library decides to break up a Blu-ray/DVD combo pack and circulate the DVD and Blu-ray discs separately (or to break up a Blu-ray/4K Ultra HD Blu-ray combo pack and circulate the standard Blu-ray and 4K Ultra HD Blu-ray discs separately), the two items must be cataloged on separate bibliographic records using the DVD only, Blu-ray only, and 4K Ultra HD Blu-ray only MARC templates. In order to avoid incorrect matching when other libraries are batch importing, the UPC for split DVD/Blu-ray sets (and split Blu-ray/4K Ultra HD Blu-ray sets) should be in the =024$z (not =024$a). Including a subfield $q noting that it is for the set is also helpful. Finally, add a =500$a note similar to "Originally released as part of a Blu-ray + DVD combo pack" or "Originally released as part of a Blu-ray + 4K Ultra HD Blu-ray combo pack."