The review into Len Brown's extramarital affair with council adviser Bevan Chuang uncovered a large number of telephone calls and text messages the Auckland mayor made to five unidentified numbers.
Last night, Mr Brown declined to identify the numbers, saying the information was not held by him and details of his phone calls were private to him.
Papers released under the Official Information Act show that of the 25 telephone numbers with the highest frequency of calls and text messages from Mr Brown, six could not be attributed by the council to a person or company.
Council telco analyst Tracy Findlay did recognise one of the six telephone numbers as that of a female member of the mayoral team.
"The rest of the numbers were not located on our Vodafone or Telecom account," she said in an email to Michael Quinn, the executive officer for then chief executive Doug McKay.
The papers show EY (Ernst & Young), which undertook the review and found Mr Brown did not inappropriately use council resources during the affair, sought all of his telephone records from the council.
Yesterday, Mr Quinn said he did not know whom the unidentified numbers belonged to.
"EY were pretty satisfied they had identified all the individuals so they could put names to the telephone numbers on the mayor's list, but I don't know who they are because we were never supplied with that information," Mr Quinn said.
Under the terms of reference for the review, EY held the information, analysed it and provided the council with the report.
Mr Quinn said that for privacy reasons, it would not be possible for the council to obtain the top 25 numbers called by the mayor and release them to the Herald.
In its report, released on December 13, EY said Mr Brown made 1375 calls and texts to Ms Chuang out of a total number of 13,797 calls and texts between November 19, 2010, and October 21, 2013.
Ms Chuang told EY all of Mr Brown's calls and texts were of a personal nature. The mayor said two-thirds of the calls and texts to Ms Chuang were of a personal nature, the report said.
The council policy on the use of mobile telephones allows the mayor and councillors to make personal calls, but costs are required to be reimbursed. The EY report said Mr Brown made one reimbursement of $263 on October 25, 2012, for personal use for the 2011-2012 period.
The council paid $4538.50 for the mayor's mobile phone calls and texts over the three-year period.
EY said it was not possible to calculate the costs of personal calls and texts to be reimbursed by Mayor Brown, but it was theoretically within the range from nothing to $2898.77.