Is the Sheriff of NSW a valid lawful office?

How is it that the sheriff in NSW has any power if the empowering instrument creating the Sheriffs function ceases to have effect? Where is the power to override the prerogative instrument of the King within Australia's Constitutional Monarchy?

A Brief History of the Charter.

As a result of the criticisms of the existing judicial arrangements in New South Wales by Commissioner Bigge the Court of Criminal Jurisdiction and the Supreme Court of Civil Jurisdiction were abolished in 1823. The New South Wales Act, 1823 (4 Geo. IV Act No .96) gave power to the King to issue letters patent or a charter to establish a Supreme Court in New South Wales and to settle the details of jurisdiction. Such letters patent were issued on 13 October 1823 and constituted the Supreme Court a Court of Record, and provided for the appointment of a Chief Justice, Registrar, Prothonotary, Master and Keeper of the Records and for the admission of Barristers and Attorneys. It also prescribed the names of appointment and the duties of the Sheriff. The Charter took effect in New South Wales on 17 May 1824. The Supreme Court received jurisdiction in all pleas, civil, criminal and mixed, and the jurisdiction of the Courts of Kings Bench Common Pleas and Exchequer and Courts of Oyer and Terminer and General Gaol Delivery.

The Supreme Court was also given the equitable jurisdiction of the Court of Chancery and ecclesiastical jurisdiction in probate matters. The Australian Courts Act, 1828 ( 9 Geo. IV Act No .83), repealed the New South Wales Act, 1823 which was a temporary Act, and added to the Supreme Court the common law jurisdiction of the Court of Chancery. This Act itself was originally passed for a period of seven years but was eventually made perpetual by the Acts 5 & 6 Vic. c.76. Originally in 1823 it was provided that if both parties to a civil action were so desirous the Act might allow the appointment of a jury. In criminal cases all trials were to take place before judge and jury of seven military or naval officers.