Minimum set of fields beside HB.import_ref for successful record update

[nobthenob]

Hi,
I am trying to update some existing records in the HB database using a CSV file.
I understood, that the HB.import_ref field is the record identifier.
So I tried to update just a view fields of a record with a CSV file, that contains HB.import_ref plus a few additional fields.
Homebox said the import was successful, but the fileds were not updated.
I suspect, that beside HB.import_ref, some other fields are mandatory for the import.
The documentation on the import function does not provide this information.
Does anybody know the answer?
Thx, nob