My personal details are confidential. Can I invoke my duty of confidentiality (e.g. as a civil-law notary)?

No. In such cases no duty of confidentiality may be invoked, unless this duty is based on international regulations; see Article 33 (4) of the Statistics Netherlands Act. Moreover, the data received - by the Director General of Statistics in connection with the performance of the duties for the implementation of the Act - may be used solely for statistical purposes.