One of the most common symptoms of Covid 19 - a sore throat - is not listed on the card everyone must fill in before being allowed into the country.
The card is a crucial part of the country's border controls and questions are being raised about how authorities got it wrong.
As part of government demands for "watertight" border controls, a new arrival card was introduced at airports on 20 March.
The card twice prompts passengers: "Have you had any of the following symptoms in the past 14 days: Fever? Cough? Difficulty breathing?"
National MP Dr Shane Reti noticed an omission.
"Turns out that New Zealanders haven't had difficulty breathing as one of the main symptoms, they've had a sore throat," Reti said.
"Fifty percent of New Zealanders have had a sore throat. So really, a sore throat should have been on the new arrival card and we've missed that boat.
"That concerns me for the people who have come into New Zealand and been screened in the wrong way."
Difficulty breathing was a late symptom of the virus, and sore throat an early one, he said.
"Tens of thousands [of people] have been screened with the wrong screening questions."
Reti showed the card to Auckland University professor of medicine Des Gorman.
"The card is flawed," Gorman said.
"Difficulty breathing is a lot less common than a sore throat.
"I mean, if you're going to retain it, that's fine, but a sore throat certainly needs to be there ... sore throat presents in about half of cases."
Ministry of Health said the cards were used to identify individuals with virus-type symptoms.
"... raised temperature, cough or difficulty breathing and the focus is on these symptoms which most obviously help to identify Covid-19," it said in a statement.
It would be reviewing the symptoms listed on the cards at their next reprint, it said.
Anyone arriving from overseas had to go into 14 days managed isolation, it added.
Reti said the mistake may have let the virus in among the thousands of returned travellers who used the card in the three-week period between the card being introduced, and mandatory managed isolation being imposed on 10 April.
"Nothing we can do about it, here now. But certainly looking forward, our prime screening mechanism at the border should be accurate."
"You'd want people who present with just a sore throat to definitely have a nasopharyngeal swab taken.
"So it's going to miss a very important group of people who need to be surveyed."
The Customs Service and Health Ministry must collaborate to redo the card, Reti said.
The MP is proposing to reopen the border to international students for the second semester in July, if they undergo quarantine, and "if we open the border in a protected way ... our arrivals card has to be perfect".
The Customs Service said the Health Ministry listed the symptoms on the arrival card.
Gorman wants to know how the mistake happened.
"I think they need to explain how they got this wrong.
"Was it a typographical error? Was it an insight error?
"There needs to be some examination of how a card there could be so important could end up in such a flawed state."
The remedy, though, was simple. "Throw it away and start again," Gorman said.
The ministry has not said how a sore throat was left off the cards as a symptom.
Face-to-face assessments were now taking place with returned travellers, who were asked if they had a "cough, sore throat, shortness of breath, any cold or flu type symptom, or loss of sense of smell ... in the last 14 days", it said.
Its website states effective border control is even more important under alert level 2.