Six thousand drivers' details should not have been posted the same day it was revealed 25m people's details were lost, an agency chief has admitted.
The drivers' details were on two discs
Brendan Magee, head of NI's Driver and Vehicle Agency, said he would now "clearly have to look" at his own position.
The DVA sent the unencrypted data to its headquarters in Swansea.
They were sent the day it was reported 25 million child benefit records went missing in the post.
In the latest incident, details of 7,685 vehicles and more than 6,000 vehicle keepers were lost.
The data includes the keeper's name, address, registration mark of the vehicle, chassis number, make and colour.
It was sent out on November 20 and 21, when the lost child benefit discs sent by HM Revenue and Customs came to light.
On Wednesday, Mr Magee said: "With hindsight, we should have stopped any data going anywhere from that day - I fully accept that."
He added: "I clearly have to look at my own position. I fully accept that, and that is a matter for me in discussion with other people.
"But I also want to put into context that what actually happened at Revenue and Customs... the level of personal information here is not on the scale of Revenue and Customs.
"The amount of information going out certainly isn't - 6,000 compared to 25 million."
Northern Ireland's Environment Minister Arlene Foster said the discs were dispatched on 20 and 21 November and both arrived in Coventry.
However, on 5 December the DVA was told that the discs had not arrived in Swansea.
Ms Foster said she was "not optimistic" that the discs would be found.