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The correspondence should have been included in material released in February through Health Minister Tony Ryall, but Mr Hundleby said its absence was a matter of "cock-up rather than conspiracy".
Although it had been informally acknowledged earlier this year that the newspaper had not received all of the correspondence sought, repeated requests about the issue brought no tangible response until this month.
The newspaper sought the correspondence after concerns were raised in Parliament by the then Labour health spokeswoman, Ruth Dyson, about Canterbury neurosurgeons' dissatisfaction with the plans for the South Island service.
It was suggested Canterbury neurosurgery clinical leader Martin MacFarlane would retire from the profession if the announced model for the service was imposed and another neurosurgeon, Ronald Boet, would resign.
It made the request for correspondence to both the National Health Board and the Canterbury District Health Board, but the Canterbury board referred the request to the national body.
The material released in February all related to correspondence between the expert panel on neurosurgery and Canterbury District Health Board representatives before the panel's decision was announced in November.