The Chief Electoral Officer says voting irregularities such as those found in the Waitakere electorate are not uncommon though police could be called in to investigate.
A judge has found that some people in the Waitakere electorate appear to have voted more than once and almost 400 people voted despite not being on the electoral roll.
Chief Electoral Officer Robert Peden says un-enrolled voters account for about 10% of all special votes and this occurs in every electorate in every election.
Mr Peden also says duplicate votes are also unfortunately quite common, with 480 dual votes recorded in the 2008 elections.
He says 58 people have been referred to the police.
The Waitakere seat was won by Paula Bennett by a margin of nine votes, following a judicial recount.
On election night Ms Bennett had been ahead by 45 votes but following the counting of special votes had lost to Labour's Carmel Sepuloni by 11 votes.