Cabinet signed off tough new measures to tackle gangs on the basis of inaccurate information which over-estimated the scale of the crime problem.
The briefing paper told ministers 4000 gang members alone were responsible for a huge number of drug and violence crimes, including murders.
The release of the document through the Official Information Act followed the earlier discovery the wrong information had been used in a press release to justify the policy.
Cabinet ministers were also given the wrong information.
The information, which appeared to have been provided by police to the minister's office, went before Cabinet in June before the August announcement.
The new measures passed by Cabinet were targeted at gang members who were said to be responsible for huge levels of criminal activity. They also show the Government contemplating greater powers for police to tackle gang activity.
Sociologist and gang researcher Dr Jarrod Gilbert outed then Police Minister Anne Tolley over the inaccurate press release and said it was "absurd" the wrong information had also gone to Cabinet. "This was an error of epic proportions. The problem by comparison is almost insignificant."
The inaccurate figures had suggested the 4000 gang members in New Zealand were personally responsible for about 1500 serious violence and drug charges. New figures show this year gang members were actually responsible for 26 of the 649 serious drug charges laid. They were also responsible for 61 of 868 violence charges.
The difference between the sets of figures is the inaccurate figures which resulted in police excluding potentially 56,000 other people who might have been responsible for the crimes by attributing the actions solely to gang members. Police had failed to mention a wide group of gang prospects, general associates and family of gang members.
Mr Gilbert said the new and accurate figures showed a different approach was needed for gang crime. "It is a community issue. There are different ways of tackling it."
Labour police spokeswoman Jacinda Ardern said the inaccuracy raised concern about whether the Government's plan to tackle gangs would work. "You've got to make sure you are making evidence-based decisions. Ultimately, people want [politicians] to be effective."
The office of Police Minister Michael Woodhouse did not respond to questions as to whether Cabinet needed to consider the matter again. Asked if the minister's office accepted the figures were wrong, a spokesman said: "It is unfortunate that some figures required clarification."
gang members responsible for
serious drug and violence crimes from January to April this year.
26 out of 649 serious drug charges laid this year were against gang members.
61out of 868 violence charges laid this year were against gang members.