"All sales at excessive variance to roll values are reviewed and inspected as part of our normal processes to ensure that our property information is correct," he said.
"These variances can often be accounted for by the fact that recent building work is not yet included in the rating valuation and/or market movement since the revaluation date."
Critics say all ratepayers miss out when properties are valued too low, but Mr McKay said the system was set up to cope with changes.
"Each year we update values where there are physical changes to properties, i.e., new building work and where new properties are created as a result of subdivision. In these instances the updated values are back dated to July 1, 2011 to maintain value relativity with all other properties," he said.
This was the fairest system.
In October, homeowners began complaining about the new valuations, citing significant disparities in their areas and saying they were puzzled and angry about low or inconsistent valuations.
Residents from Mission Bay to Takapuna accused the council of under-valuing their properties and damaging resale chances
Judith Pohn, of Mission Bay, said her house was in good condition, and she could not fathom the valuation plunge from $690,000 to $550,000 when she sought to sell for $734,000.