The Fire Service Commission says industrial action by firefighters has caused inaccuracies in its annual report.
The commission says the action, by about 2000 career firefighters in support of a pay claim, compromised the ability of the Fire Service to function in a fully effective way.
Commission chair, Dame Margaret Bazley, says it was deeply disappointing that the action was taken, from September to December 2009.
The action, which ended with the signing of a new collective contract, initially involved banning the use of computers, but escalated to only providing activities related to emergency response and operational readiness.
The result was that no new incident data was available to report on progress against the Fire Service's national goals.