Rectification of record errors: authorities may correct apparent mistakes within specified timeframes, subject to natural justice. Section 161 authorises an issuing authority to correct errors apparent on the face of its decisions, orders, notices, certificates or other documents on its own motion or when notified by an officer or the affected person, normally within three months of issuance. Rectification is barred after six months except for purely clerical or arithmetical corrections arising from accidental slips or omissions. Any rectification that adversely affects a person must be undertaken following the principles of natural justice.