There might be hundreds of border workers who aren't being regularly tested despite potentially coming into contact with people, ships, planes, or other things that have come to New Zealand from overseas.
And workers who are being tested can go 12 days without a test and still meet the weekly testing requirement, or 26 days without a test and still meet the fortnightly requirement.
Today's case of an Auckland airport worker is a timely reminder of the importance of such tests, which can catch a case early before it has a chance to spread in the community.
The Government ideally would have eyes on everyone in MIQ and at the border who needs to be tested, and whether these tests are being done.
It does not.
This is a vulnerability in a system that everyone thought was tip-top until last week, when MBIE revealed that a Grand Millennium security guard, Case B, hadn't been tested for five months.
He was apparently lying by telling his employer, First Security, that he was being tested fortnightly.
First Security or the Government could have checked whether that was actually happening by looking at the border worker testing register - but neither did.
This is the hole - not only in MIQ but across the whole border testing regime - which prompted National MP Simon Bridges to liken the system to an honesty box at a roadside feijoa stall.
The Government concedes that the checks and balances need to be better.
Taking unvaccinated workers away from the frontline from the start of May will help, as will the new public health order that takes effect from 11.59pm tomorrow.
Currently border workers requiring weekly testing must have a test at least once within a seven-day period. This means they could go 12 days - or 26 days, if they need fortnightly tests - without a test and still meet the requirements.
Under the new order, workers requiring weekly testing will need to be tested within seven days of their last test.
The order also adds baggage handlers and workers who come into contact with "affected items" - such as the LSG Sky Chefs worker who may have caught Covid-19 from handling linen from incoming flights - to the list of those who must be tested.
And from next Tuesday, April 27, all border employers will be required to use the Government's border worker testing register. Currently, only about 60 per cent of them do.
But the register only tells us when workers have been tested, not when they should be tested.
Employers - public and private - are legally required to keep a record of who needs to be tested and when, which essentially makes them the Government's eyes on the border workforce.
But the onus is on the Government to ensure compliance, and whether it's doing enough - balancing issues such as privacy and practicality - has been the subject of some resistance.
Ankle-bracelets for border workers is too Big Brother-ish, said Covid-19 Response Minister Chris Hipkins.
The Government can't be expected to be on every street corner checking that every car is keeping to the speed limit, PM Jacinda Ardern said.
But is it on any corner at all? What spot checks have been done, if any? Is there even a compliance team checking up on the border-wide system?
One check that's been live since February is the "WhosOnLocation" register at every MIQ facility where workers sign in and out. That can then be matched against the border worker testing register to see if workers are being tested as frequently as they should be.
It's not foolproof - Hipkins said Case B wasn't signing in - but if it improves compliance, why not look into rolling it out to ports and airports?
Why hasn't there been a system-wide audit, followed by fining any worker missing tests and any employer failing to keep proper tabs on their workers?
Is the $300 infringement fee or $1000 court-imposed fine enough of an incentive to follow the rules?
Confidence in the system has been shaken, and it's unlikely to be reassured by MBIE boss Carolyn Tremain writing to MIQ employers last month to remind them of their legal obligations, nor by Hipkins sending a similar letter tomorrow.
More worryingly, Tremain couldn't say what compliance checks, if any, had happened since September, when regular testing became the law.
In the fallout last week, Hipkins revealed the results of recent sampling that showed 90 per cent compliance from the 4500-strong MIQ workforce, and 98.4 per cent compliance if the testing timeframes included some leniency beyond the required timeframes.
Seventy-four MIQ workers hadn't been tested.
If we apply that rate of non-compliance to the 15,000-odd border workers - including MIQ workers - who need to be regularly tested, there could be about 230 workers who are missing their tests.
More importantly, it begs the question of why such sampling wasn't being done earlier, and isn't being done across the whole border rather than just MIQ.
That would at least give us an idea of the size of the problem.
The Herald has asked how many border workers are missing their tests. The query bounced from MBIE to Customs to DPMC to Health.
No one seems to know.