In this field - Location and inventory number of unique thing -, subfield $a is used for the place and the (abbreviated) name of the organization; subfield $b contains the inventory number of the unique thing. We use this field in the CBS MARC 21 format because there exists no proper equivalent of this field in the MARC 21 format (March 2020).
This field has no indicators and no subfield $6 - Link - (PICA+ subfields $T and $U).
In the export of CBS MARC 21 records (to WorldCat), subfield $b is converted to MARC 21 field 245 - Title Statement - subfield $f - Inclusive dates -. This is done to prevent incorrect merges of records.1
1. This needs to be checked (March 2020).