Is it about Oversea Investment (OIO) declaration or bright-line tax declaration? OR Is it about money laundering?
It is important to find out what the document is, sometimes IRD or OIO or Ministry of Internal Affairs investigate law firms, after they do auditing. Maybe your file is one of their audit files?
Under the law, your conveyancing lawyer will have to provide the documents to them and to answer all their audit questions. Privacy and confidentiality do not apply to those statutory bodies.
If I were you, I will be more interested to know why need to sign something after about 1 year?