A new report into the exaggeration of breath test figures has found an extra 400,000 cases, bringing to number to almost two million.
The Policing Authority has asked independent consultants Crowe Horwath to examine the breath test debacle, as well as the errors in Fixed Charge Penalty Notices.
It was originally suggested that one million false breath tests were recorded.
The report has also found that Garda management did not respond to the breath test problem appropriately.
Irish Examiner correspondent Mick Clifford says the number of breath tests has risen twice.
He said: "The fibs get bigger and bigger because when the report came out it emerged that there was an extra half a million of these fake breath tests.
"The leaks from today's report suggest we can throw another 400,000 on top of that, so we are heading towards two million fake breath tests over a seven year period between 2009 and 2016."
Meanwhile, Fianna Fail justice spokesman Jim O'Callaghan has called for beefed-up oversight powers for the Policing Authority amid reports that the bogus breath test scandal is worse than previously thought.
It is believed another 400,000 false breathalyser records were put on the force's database on top of the near 1.5 million identified in an internal audit.
One senior officer previously revealed that 6.4 million breath tests were inaccurately recorded at one stage but it was not deliberate falsification and was corrected overnight.
The report for the Policing Authority by accountancy and business consultancy firm Crowe Horwath is expected to criticise the way the controversy was initially handled by senior management but also to raise concerns about the culture in the force.
It points to implicit demands on officers for bigger and better breath test numbers rather than an explicit direction from management.
Garda chiefs have been asked to launch further investigations into 2,134 drink and drug-driving checkpoints and associated data which contributed to the massive over-exaggeration from 2009 to 2016 which recorded 3,498,400 breath test records on the Pulse system when only 2,040,179 were carried out.
Mr O'Callaghan said the problems in the Garda could be greater than envisaged and it is crucial new oversight powers are created.
"Full public confidence in the processes and procedures around Garda oversight is a critical component of effective policing in Ireland," he said.
"Unfortunately, the poor performance of senior management in An Garda Siochana remains at the fore of these repeated controversies."
Mr O'Callaghan said the public should get a more detailed account of the scale of the falsification of breath test data when the Policing Authority is called before the Oireachtas Justice Committee.