Kia ora Sam thanks for fixing the addresses. You can inspect the history of the address nodes to see the source used is was LINZ (Land Information New Zealand). That is likely what is also used by Google Maps. I can see that the LINZ dataset is different to what is in the Auckland Council address dataset (AC is more similar to your correction). Unclear to me why they differ, because my understanding is that LINZ gets its address data from the councils.
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            Published using OSMCha: https://osmcha.org/changesets/154501273
            