The government is allowing isolation facilities to be overbooked so full capacity is reached even if there are last-minute cancellations or no-shows.
The government has been using 32 hotels to house people for their 14-day stay in managed isolation after entering New Zealand.
In early November, those who were keen to come back to New Zealand for Christmas were warned about available spaces filling up.
Just three days later, it was announced all spots were fully booked, up until Boxing Day.
It led Air Commodore Darryn Webb, who heads Managed Isolation and Quarantine, to add 100 extra rooms between 13 and 23 December, to accommodate more people.
Minister for COVID-19 Response Chris Hipkins says the supply of rooms was enormously constrained by the number of hotels they were running.
To ensure there were no empty rooms from cancellations, they were overbooking the hotels, he says.
"We're allowing for a little bit of overbooking on the basis that we do know we get a proportion of no-shows," Hipkins says.
"So we can dip into the contingency that we have, and take a bit more risk on overbooking the system, on the basis that we know we'll be able to accommodate that."