If there are two records in Alma, one that has 020 $a u and another that has 020 $a v and 020 $z u, the both records will be related by the system with the relation: Replaces/Replaced by. The 020 $z is understood as a "cancelled" ISBN and therefore included in the job that calculates the relations.

In the vast majority of cases we know 020 $z is a false/invalid ISBN: a publisher mistakenly(!) uses the same ISBN in two different resources that have nothing to do with each other. However, according to the international rules for describing resources, the erroneously printed ISBN information must also be recorded in the catalogue record (MARC field 020 $z) so that the resource can be searched using all the information it contains.

Linking these two works is completely senseless from our point of view as the resources have nothing to do with each other. Furthermore it is confusing for our users - especially regarding the relationship: Replaces/Replaced by.

We have no examples to support your view of 020 $z for "cancelled" ISBNs and we therefore ask you to remove 020 $z from the relation keys.