Could you pay attention to https://issues.folio.org/browse/UIU-1870. In API we should have all necessary data. How we understood now 1 field are absent. Could you please correct me if i am wrong?
Patron group (from User information record),
volume (from the Item record)
enumeration (from the Item record)
chronology (from the Item record)
copyNumber (from the Item record)
We can use tree structure for data, example below: