[tfm]

Official local datum is GDA94, which is usually within about a metre of WGS84. /me pats pocket protector

I think the idea here though is that the underlying terrain has scooted around a bit in the last twenty years, so a new datum would save on the need to print new maps and update the databases containing trig points and such. New coordinates can be labelled as explicitly aligned to the new datum, get some versioning happening.

Unfortuately it seems impossible to confirm this, because the Geoscience Australia website does not appear to make any reference to this purported new effort that's been making the rounds of late. New website layout, maybe their CMS is broken.

[ellisv]

This is similar to the difference between WGS84 and NAD83 (North American Datum 1983). WGS84 is defined by the average of stations world wide while NAD83 is defined in a way that it is relatively constant across North America. NAD83 initially matched WGS84 but their difference increases each year by a small amount (negligible for most consumer use). Of course there are other differences between NAD83 and WGS84 as well (reference ellipsoids) and often they are treated as the same by non-cartographers.