NRC chairman Bill Shepherd told ratepayers who had paid the invalid rates they would not be refunded and would have to seek a separate court ruling if they wanted it back.
He said an appeal to the High Court's ruling was being considered.
Mr Shepherd confirmed rates' notices for Whangarei and the Far North ratepayers during the five-year period also did not state a calendar date by which each instalment of rates was to be paid. They would also likely be ruled invalid if those ratepayers took the issue to court.
Mr Shepherd did not reply to questions by edition time on whether NRC would write off the rate arrears from Kaipara as well as in Whangarei and the Far North.
Kaipara ratepayer Bruce Rogan, who as a party to the High Court proceedings, said heads needed to roll over the invalid rates debacle.
"The ratepayers who have been victimised and vilified for questioning the competence of councillors, and their compliance with the law and who have always shown good faith and willingness to come to reasonable terms are not the culprits here."
Mr Rogan said Mr Shepherd and NRC chief executive Malcolm Nicolson have no one to blame but themselves for what has happened, and the region's ratepayers should hold them to account.
New Zealand Taxpayers' Union executive director Jordan Williams said Kaipara ratepayers would score an own goal if they forced NRC through court to refund the rates and penalties.
"The costs involved in going to court aren't worth pursuing a refund. Even if a refund is ordered, the council can raise rates the following year and recoup its cost."
Mr Williams said should Kaipara ratepayers decide on a class action to recover the rates, the union would consider joining as a party.