In th books collection there are records which are separate volumes merged in one record. In order to migrate them we would need to catalogue them as separate records. As the data is not fully consistent, we need a human oversight on this task.
The records in question:
https://cds.cern.ch/search?ln=en&cc=Books&sc=1&p=596%3AMULTIVOLUMES*&action_search=Search&op1=a&m1=a&p1=&f1=