Violent and sexual offences are among the thousands of reported crimes not being recorded by two Welsh police forces every year.
HM Inspectorate of Constabulary (HMICFRS) found there was a failure to properly record more than 8,400 crimes in total.
As part of rolling inspections, every force has its crime data checked.
Gwent and Dyfed-Powys Police were found to have made improvements in recent years but there were still failings.
The independent inspections looked back at the last four years and found:
- Every year, more than 3,300 reported crimes are not recorded by Dyfed-Powys Police, which is 12.2% of its total reported crimes. These included sexual offences, public order and violence offences.
- Although its rate is lower at 9%, Gwent Police failed to record more than 5,100 reported crimes each year.
DYFED-POWYS 'CONSISTENTLY MISSED' DOMESTIC ABUSE CRIMES
Dyfed-Powys had made a "concerted effort" to record crime more accurately since the last report in 2014, particularly in dealing with more complicated crimes like modern slavery and sexual offences, HM Inspector of Constabulary Wendy Williams found.
But it was a "cause of concern" that the recording rate for violent crime was only 84.4% and the report said the force must improve.
Ms Williams said: "In many cases, victims only get the right to essential support services when a crime is recorded.
"That's why I was concerned to see that the force consistently missed crimes related to domestic abuse, stalking and harassment off the book."
The inspection suggested that officers and staff not understanding the crime-recording rules led to the failures, made worse by limited supervision to correct these decisions as soon as possible.
Dyfed-Powys Police in response said it recorded 93% of reported sexual offences.
Temporary Deputy Chief Constable Richard Lewis said: "The report recognises the good progress made by the force and the unequivocal desire to support victims of crime.
"There has been a programme of improvements to the way that crime is recorded, which is ongoing and is overseen by chief officers.
"This has already identified areas of good practice, recognised by HMICFRS and further steps have been taken since the inspection to improve the recording of domestic abuse through increased supervision and revision of processes."
'A FEW TEETHING PROBLEMS' AT GWENT POLICE
In the Gwent force area, Ms Williams praised improvements and strong leadership on crime-recording and was "confident" victims were at the heart of crime-recording decisions.
But she found "a few teething problems" including that call handlers were not always taking down all the details they needed.
There was also "more to do" with reports of domestic abuse.
"But I know that the force has already put together a comprehensive plan to make sure it does better for victims of this terrible crime," she said. "We have seen that Gwent Police is committed to putting the work in, so I am confident the force will take the necessary action to improve."
A Gwent Police spokeswoman said: "Forces across the UK operate differently and currently in Gwent at the first point of contact there are 33 crime types that are immediately 'crimed' by our operators with officers 'criming' anything outstanding on further investigation.
"We are in the process of introducing new measures where all crimes will be recorded at the first point of contact including violent crime and our training programme will commence in January."