Some of the 10,000 people wrongly dropped off the invitation list for bowel screening may have been waiting to be seen for five years, the Ministry of Health says.
Those people were among more than 12,000 people inappropriately withdrawn from the Waitemata bowel screening pilot programme because their addresses on the National Health Index were not current.
The full national bowel screening programme is being unrolled across the country over the next few years.
Ministry service commissioning director Jill Lane said officials did not know "exactly" for how long the 10,000 people wrongly struck from the screening list had been withdrawn.
However, a briefing paper to Health Minister David Clark in November, released under the Official Information Act, showed 10,349 people were excluded and had to be put back on the recall list last year, so they could be re-invited to participate in the screening programme if their NHI addresses were updated.
None of the ministry publicity around the flawed invitation process and the recently ordered review of the trial screening programme refers to the 10,000 people.
While the briefing paper suggests the invitation error was only discovered in September last year, both interim and final evaluation reports of the pilot programme show there were concerns about the currency of address information and the limits on the register being used for the pilot.
Both evaluation reports said it was intended the NHI numbers be supplemented by Primary Health Organisation (PHO) enrolment data (information from GP practices) but "due to logistical reasons this did not occur".
Recent reporting from RNZ on correspondence between the Waitemata District Health Board and the ministry showed concerns about the register were raised by the board over several years.
Asked what had been done to try to contact the 10,000 outside of using the NHI, Lane said the Waitemata DHB had checked names from returned mail against Waitemata PHO registers and the DHB's own patient management system, and run advertising campaigns asking those who were eligible to participate but who had not been invited to contact the DHB.
When announcing a review of the national bowel screening programme in February, Clark apologised for the invitation botch-up, outlining the efforts to contact and re-invite about 2500 people who had been withdrawn but had since had their addresses updated in the NHI.
Eight people who had updated addresses but not been invited to participate were later found to have cancer.
A clinical review of the cases found that for five of the eight (two of whom had died) screening would not have altered their clinical outcomes.
For the other three, including one person who had died, it was considered earlier diagnosis was in their best interests, but it was not possible to determine if screening would have improved their prognoses.
The independent review of the programme ordered by Dr Clark and led by Prof Gregor Coster is to report back in June.
It will explore the pilot invitation issue, determine how well positioned the national programme is for successful delivery, and what changes might be required.