A person was diagnosed with bowel cancer more than 3 years after they should have been invited to take part in a free screening programme.
Two other patients also missed were diagnosed with cancer 33 and 25 months after invitations should have been sent. One of the group died.
A review carried out for the Ministry of Health was unable to say what, if any, effect being missed from screening had in the three cases.
The ministry did not reveal the diagnosis timeframes for the three patients and initially refused to do so when asked by the Herald. The Ombudsman intervened and the information has now been released.
Special report: New Zealand's bowel screening programme
• Bowel screening programme misses too many cancers, says expert
• 'All clear' brochure may have falsely reassured ill patients
• Bowel cancer society wants more information
In response, Bowel Cancer NZ says it's likely the patients would have had a lesion present at the time they should have been invited to take part in screening.
"It is likely given the normal timelines for cancer growth that if screened then they may have had better outcomes," said Frank Frizelle, the group's medical advisor, surgeon and bowel cancer expert.
"This administrative error removed them of this opportunity."
Problems with how addresses were updated on an IT system used during a pilot in Waitemata meant thousands weren't invited to participate in free screening.
Eight people wrongly missed from screening later learnt they had bowel cancer.
Clinical records were reviewed by Dr Maree Weston, a consultant colorectal and general surgeon at Counties Manukau DHB.
When mail was returned and no alternative address could be found the people were removed from the screening pilot.
At a later point they came into contact with the health system - such as at a GP or accident and emergency clinic - and their address was recorded in the National Health Index (NHI) system.
However, the screening pilot couldn't access that NHI information, and a new invite was not sent out.
"It is my opinion that in 5 of the 8 cases there is no possibility that offering a screening test at the time of their address being updated would have altered the outcome for those patients," Weston's November 2017 report stated.
"With regards to the remaining patients...a significant amount of time had elapsed between the date of their address update and the date of diagnosis of cancer (33, 41 and 25 months respectively).
"While earlier diagnosis for these patients would have been ideal, it is impossible to conclude that an earlier diagnosis would have been made or that a premalignant polyp would have existed at the time interval mentioned."
Weston noted only 54 per cent of people invited to screen did so, and there was also an unknown false negative rate. That meant "no guarantee these patients would have accepted the screening offer and then had a true positive test result...it is impossible to prove any impact".
In April the ministry said it had discovered another problem that meant many more people may have been missed out from the Waitemata pilot, which ran from 2011 until the end of last year.
More than 30 people had developed bowel cancer, the ministry said, and work was ongoing to determine what, if any, difference being missed from screening made in those cases.
In an update provided to the Herald, Dr Jane O'Hallahan, clinical director of the ministry's national screening unit, said clinical review had found screening was unlikely to have made any difference in most instances - however in at least three cases it may have.
"It was determined their cancers may have been detected earlier if they had been offered, and accepted, an invitation for free bowel screening. These cases are undergoing further peer review before the people concerned are contacted by the ministry via their GPs and offered an apology."
That brings the number of people who may have caught their cancer earlier had they been included in screening to at least six.
Each year more than 3000 New Zealanders are diagnosed with bowel cancer and more than 1200 die from it. There can be no warning signs cancer is developing, and early detection is critical.
Under the national programme, screening will be offered every two years to men and women aged 60 to 74.
Following the initial pilot in Waitemata, free screening is currently in five DHBs, with the other 15 to progressively join, with the entire country covered by 2021.
The independent review of the programme ordered by Health Minister David Clark was released this month and found, overall, the roll out was progressing well.
The review found Waitemata DHB staff became aware of the limitations of the IT system early in the pilot, and raised those with the ministry. However, applications for funding to fix those issues were declined.
Bowel Cancer NZ spokeswoman Mary Bradley said the ministry needed to act urgently on the review recommendations, particularly in regard to workforce capacity problems.
"Workforce capacity is a key factor in delaying the rollout to all DHBs which means we will be waiting until 2021 for the last DHBs to offer screening."