Juvenile justice authorities in Western Australia have been unable to verify how much time children are spending locked in their cells because of issues with a reporting system.
The prolonged confinement of detainees at Banksia Hill, the state's only youth detention centre, has been heavily criticised by advocates and legal observers.
WA's Supreme Court last year found a teenage boy had been unlawfully locked in his cell for at least 20 hours per day on 26 occasions over six months.
A class action launched in the Federal Court on behalf of past and present detainees alleges a teenage girl with autism was confined up to 23 hours a day.
The state government has said lockdowns are only used as a last resort when there are critical incidents or staff shortages.
But at a parliamentary committee hearing on Wednesday, officials from the Department of Justice conceded they did not have reliable data recording of out-of-cell hours at Banksia Hill during the last financial year.
"We do have records of out-of-cell hours but a lot of the time we can't actually, hand on heart, say they were 100 per cent accurate," director-general Adam Tomison told the hearing.
"We've actually conveyed that to varying bodies, including the Children's Court as needed.
"We've instituted other processes to try and better track out-of-cell hours."
Dr Tomison said issues with the monitoring process had come to light partly because of various legal actions filed against the department.
He said Banksia Hill now had staff dedicated to recording the out-of-cell hours, a requirement he described as "incredibly onerous".
"Clearly our systems weren't up to scratch compared with the level of scrutiny now required on out-of-cell hours," he said.
"I'm confident we have a reasonable regime in place in terms of tracking the recording of those hours."
A government response to a question tabled in parliament this week revealed there had been more than 1100 occasions between August 25 and November 20 last year where youth detainees spent more than 20 hours per day in their cell.
The figures included stand alone Unit 18 at the Casuarina men's prison which is housing a small number of youth detainees.
A detailed breakdown for Banksia Hill was unavailable because the database was "flawed".
