A security worker at Auckland's Grand Millennium managed isolation facility, who tested positive for COVID-19 last week, had not been previously tested since November.
Carolyn Tremain, chief executive of the Ministry for Business, Innovation and Employment (MBIE) - which oversees managed isolation and quarantine (MIQ) - made the revelation on Wednesday at a parliamentary committee.
Tremain said the worker was tested on April 7, which is when he tested positive for COVID-19. Prior to that, she said records show he was last tested in November, despite the law stating he should be tested fortnightly.
"What we have identified through the case investigation process... is that there are some inconsistencies in the recording of when testing occurs," Tremain told the Health Select Committee.
"We don't have evidence that testing has been conducted from our systems on the frequency that we would prefer it to be."
Tremain said the employee is a "relief worker", but confirmed he should have been tested fortnightly. She said MBIE is in the process of verifying the testing information, from both the employee and employer.
Tremain also revealed that only about 300 out of 589 employers across the border have been using the Government's central testing register.
"There are 589 employers across the border and about 300 employers use it," Tremain said. "I think the issue is it's not yet mandatory although that is one of the things Ashley [Bloomfield] and I have been working on to say it needs to be mandatory."
In a policy document on its website, First Security - the company the security guard works for - states it is using the national register set up by the Ministry of Health to monitor the routine mandatory testing of border workers.
COVID-19 Response Minister Chris Hipkins has said use of the register will be made compulsory.
"This will ultimately address this particular data issue and it is predominantly a data issue, rather than an issue of people being tested. But that will mean that we will then have the complete register so we will be able to have all of that information in a format that's easier to report."
Prime Minister Jacinda Ardern warned there would be "fines and reputational damage" if private employers did not oblige.
Tremain said 89 percent of MIQ workers have been vaccinated.