NavList:

Frank wrote

As I have written before (before your were following NavList, Tony), the name "Transverse Mercator" is like clickbait. You don't need the Transverse Mercator projection for anything except understanding certain old standards for mapping applications. Setting that aside, there are lots of interesting tricks for celestial navigation near the poles. It's a worthy topic, for sure! Just ignore the TM aspect.

Until  2000 NZ used the NZMG (NZ mapping grid) which was described as using a complex-number polynomial expansion. This had the advantage of exhibiting minimal scale distortion over New Zealand. However it was a projection unique to New Zealand and so could be difficult to use or program into computer software or positioning devices (eg, GPS receivers).

In 2000  a change was made to the the New Zealand Transverse Mercator 2000 (NZTM2000) projection.  I understand that NZTM2000 is less accurate than the NZMG but the change was made for the reasons given above.

The Chatham Islands uses the Chatham Islands Transverse Mercator 2000 (CITM2000) projection.

So NZ switched to an old mapping standard??????