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Publicly available health data on wait times for emergency departments, operations and cancer treatment are now six months out of date, since Te Whatu Ora was forced to pull inaccurate figures from its website.
That has caused disquiet among some clinicians and patient groups about what they say is the lack of transparency.
Association of Salaried Medical Specialists head Sarah Dalton said health data mattered because it underpinned core decisions about funding priorities and treatment for patients.
"There's not clearly communicated 'here we are, there's our destination, here's how we're going to get there', which is really critical, whether it's emergency wait times, first specialist appointments, planned care, bed block, ramping - but also vacancy rates, which absolutely feed into those things."
Dalton, whose union represents senior doctors, conceded Te Whatu Ora faced a mammoth task bringing together 20 district health boards, with a digital infrastructure that was weak, "if not broken".
It was unlikely the agency was deliberately withholding that information.
"I suspect they're probably caught between the old systems and what they're trying to put together for the new system. But more visibility about what the reasons are for that would make everyone more tolerant and a little more confident."
One of the key performance measures was the "faster cancer treatment time", calculated as the proportion of cancer patients who start treatment within 31 days of a decision to treat.
The figures for the last three months of 2022 were still provisional, but vary from 100 percent in Hawke's Bay and Hutt Valley to just 50 percent in South Canterbury.
Cancer Society chief executive Lucy Elwood said that level of inequality was a matter of life or death for some people.
"We're concerned it's not being reported publicly. Without the data it's hard to know what's happening and we rely on that data to be a strong advocate for people living with cancer."
She was so alarmed she got in touch last week with the Cancer Control Agency, which confirmed it had provided treatment statistics for the first three months of this year to Te Whatu Ora.
"At least people in the system have the data, that's a start. But we do rely on that data as well as advocates, to ask pertinent questions on behalf of patients."
Dodgy data caused embarrassment for Health Minister Ayesha Verrall earlier this year when she referred reporters to incorrect data on Te Whatu Ora's website, showing dramatic improvements in emergency department wait times in 10 regions, which turned out to be dramatically wrong.
Te Whatu Ora "paused" monthly reporting on 10 March while an independent review was conducted.
In a written statement to RNZ, a spokesperson said the agency would provide an update on its findings "in the near future", including an action plan to give the public further assurance about performance data.
"Te Whatu Ora is combining processes and systems from 29 organisations, and the review has been a great opportunity - early in our own existence - to better understand data collection and validation.
"This will assist our focus on performance of the health system as we move ahead, including to further improve the quality of public reporting."
Meanwhile, the agency's quarterly reports included a wide range of performance data.
Whangārei Hospital emergency doctor Gary Payinda said the old figures were "obviously nonsense", when some patients were waiting more than 24 hours in ED for a hospital bed.
However, he cautioned against taking any data at face value.
"It's important to track the numbers, to look for trends. But it's also important to remember that number targets, KPIs [key performance indicators] can always be gamed, to get the number you desire."
Auckland University health systems professor Tim Tenbensel agreed.
"With any sort of organisation where there's high stakes around a particular target or performance measure - if you put scrutiny on it and have significant implications for meeting it or not meeting it, you get all sorts of odd and weird distortions.
"The end result is the data becomes less trustworthy."
When the National-led government put a particular emphasis on cutting ED wait times back in 2008, DHBs pumped a lot of resources into that and they did go down for the first 18 months while hospitals "squeezed every out efficiency possible".
After that, they continued to fall - on paper, at least, Tenbensel said.
However, behind the scenes people waiting for hospital beds were put in a separate annex, and other measures were taken to make DHB figures look good.
Tenbensel said targets only made sense where the person or organisation actually had the power to make the changes necessary.
"With ED waiting times that's particularly pertinent because most of the things driving this are well beyond the control of the ED, well beyond the control of hospitals and even well beyond the control of the government."
Those factors included the ageing population and international workforce shortages, neither of which were included in Te Whatu Ora's National Performance Reporting Metrics.