A security guard who tested positive last week was previously last tested in November last year - five months ago - even though he is meant to be tested every fortnight.
The information has emerged during the health select committee this morning, when MBIE chief executive Carolyn Tremain said the last test in their system was November 20.
She said the security guard was a relief night-shift worker - who are still meant to be tested every fortnight - who worked regularly as opposed to casually.
The Herald has also learned that police were called in to track where the guard - also known as Case B - had spent money to find out locations of interest.
Tremain was fronting the committee this morning along with other officials including director general of health Ashley Bloomfield.
She said there were inconsistencies across the whole recording system for border worker testing, and MBIE was working to make sure it was complying with the order requiring the frequent testing of border workers.
The guard may have been tested more recently than November - but if so, it wasn't in the system.
National Party Covid-19 response spokesman Chris Bishop asked: "How many workers have missed tests they should have had in the border workforce?"
Tremain said she didn't know.
MIQ deputy chief executive Megan Main added: "No, we don't know the exact number. We're working towards a mandated system next week ... the 300 or so [private] employers in MIQ will have the ability to look at percentages of compliance and non-compliance in a more robust way."
After the committee hearing, Tremain said she didn't know how many employers weren't using the government register for testing at the border.
She wrote to private MIQ employers in March to reiterate their legal obligations around regular testing. Asked what checks were done between August, when the testing became legally required, and March, Tremain said she didn't have that information on hand.
"Testing percentages across facilities are high ... We've been able to verify that 90 per cent of the workers are meeting the surveillance testing requirements."
She conceded there was a "gap" in the system at the moment, but from next week the updated system would be much improved. An independent expert would also be brought in to review the system.
Main said that Case C - also a security guard - at the Grand Millennium was being regularly tested every fortnight, though she couldn't provide the date he was last tested before his positive test result.
Questioned about the lack of testing for Case B this morning, National leader Judith Collins said she was "floored" by the revelation.
"The public has been promised for months that all of the frontline border facing staff were being tested regularly.
"Now to find out he [the security worker] hadn't been tested for months - it's just unfathomable."
Bishop said it was "staggering" that Case B hadn't been tested since November.
"We had a worker meant to be tested every two weeks working for six months in MIQ without being tested. That's a huge risk to the public."
He added it was "deeply worrying" that Tremain couldn't say how many of the 300 private MIQ employers weren't using the border testing register.
"We really do need a mandatory register that every company uses so the Government can check whether people are meeting the testing requirements - which is the law.
"This should have happened last year. And here's what really worries me. The officials could not tell us how many people had missed tests. They don't know.
"There could be many other workers out there who haven't had tests who should have been getting them. That is very concerning."
Bishop said the committee hearing - where he was only able to ask two questions - was a joke, with a "20-minute lecture" about how Covid-19 is transmitted and an explanation of the end-to-end MIQ process.
He confirmed that he already knew that returnees spent 14 days in MIQ.
"The Opposition gets very few opportunities to question officials about the Covid response. To have that curtailed by, frankly, Government MPs asking patsy questions to make it easier for the officials is pretty depressing."
Bishop was visibly frustrated during the committee hearing, and at the end tried to move a motion to have the session extended for an extra hour.
Committee chair Liz Craig then closed the public session without the motion being voted on.
Later today Covid-19 Response Minister Chris Hipkins, in the weekly vaccination update, is expected to release new data about which border workers have and have not been vaccinated.
The Government has been increasingly on the back foot over its reluctance to release data including daily vaccination doses and targets, and the proportion of frontline border workers who are still to be vaccinated.
In the past week, two security guards at the Grand Millennium MIQ facility caught Covid-19 and weren't vaccinated - even though they are supposed to be at the front of the queue.
This morning the Herald revealed the Ministry of Health is urgently seeking 18 "crucial" positions for the roll-out, which the National Party says "beggars belief".
And this morning the head of Counties Manukau DHB said Auckland only has half the number of Covid-19 vaccinators it needs for the roll-out.
The Ministry of Health says it needs to scale up its workforce in line with the roll-out, which is currently prioritising border workers, high-risk frontline workers
and people living in high-risk places.
Yesterday there were no new community cases, and four border cases including one from India. The Government has temporarily suspended arrivals from India as it looks for ways to lower the risk of importing cases from there.