During 2018-19, the Administrative Appeals Tribunal (AAT) finalised 13,491 first reviews of decisions made by Centrelink across all of the welfare system's payment streams.
In that year, the maximum time it took the AAT to make a decision was 553 days, and that was for a carer payment review.
While the total number of review requests the AAT received were not provided in response to questions on notice from Senate Estimates in October by the Attorney-General's Department (AGD), disability support was the payment type with the most reviews finalised at 4,943.
AGD said there was also a total of 1,708 second applications for review finalised by the AAT during 2018-19.
One of those reviews took 1,001 days for a determination to be made.
During the same round of Senate Estimates, Senator Kim Carr highlighted the connection between the declaration by former member of the AAT Terry Carney that Centrelink's Online Compliance Intervention (OCI) robo-debt program was "unlawful" and his job being lost.
After recalling that a period of five months had lapsed between calling out the scheme and being asked to move on, Carr told AGD that Carney had previously informed the Community Affairs References Committee that he had handed down "about six behind-closed-doors AAT decisions", which found that the robo-debt scheme was illegal.
Recalling further, Carr said Carney had told the committee that Centrelink never appeals those decisions to the second level, as that's where the decision would become public.
After having the AAT conduct a search of decisions with written reasons made by Carney, the AGD provided the following answer in response to questions on notice.
"The AAT has identified five decisions made in the AAT's Social Services and Child Support Division in relation to six applications for review of decisions made by Centrelink about debts in which Professor Carney considered in detail Centrelink's online compliance intervention system in determining whether the applicants had been overpaid an allowance," AGD wrote in its reply.
AGD said a review of the decisions in question showed that the terms "unlawful and or illegal" were not used in Carney's reasoning, findings, or decision-making.
AGD was also asked how many AAT members, in addition to Carney, had determined that Centrelink's online compliance initiative was illegal, unlawful, and/or beyond power.
"To attempt to provide the information requested would involve an unreasonable diversion of resources," the written response noted.
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During Estimates, AGD was also asked if the president of the AAT recommended for Carney to be reappointed.
The department, in response, was again tight-lipped.
"The Attorney-General relies on confidential advice from the president of the AAT about the appointment needs of the AAT. There is a public interest in maintaining the confidentiality of this advice," AGD wrote in its questions on notice reply.
"Disclosure of such advice has the potential to reveal Cabinet's deliberations in respect of appointments made by the Governor-General."
When making his own public determination that the Centrelink data-matching project is illegal, former Labor Leader and now-Shadow Minister for Government Services Bill Shorten pointed to Carney's words.
"In hundreds of robo-debt appeals to the Administrative Appeals Tribunal the government accepts the claims with the result that judgement cannot be given on the legality of the scheme," Shorten continued.
"Little wonder, given many prominent lawyers including former AAT member Terry Carney have given the opinion the scheme amounts to illegal extortion."
Earlier that week, Shorten called robo-debt "harsh and inaccurate", likening the scheme to having the same essential logic and ethics of a mob standover.
"I have consistently expressed my view that the legal foundations of robo-debt -- a reverse onus of proof on alleged debtors over often inaccurate figures -- are very shaky indeed," he said.
Services Australia last month provided updated statistics on the OCI program, confirming that from 1 July 2016 through 31 August 2019, there had been 1,159,662 assessments initiated.
Services Australia and its predecessor, the Department of Human Services, over this period raised a total of 617,018 debts. One assessment could however, lead to multiple debts if the recipient was the beneficiary of different types of income support payments, the department said. The average debt was AU$2,630.
There have been 9,511 formal reviews requested, with 8,412 completed.
Similarly, there have been 1,961 appeals requested and 1,644 of those completed.
The number of debts reduced to zero is 27,123, and the number of debts waived and/or written off permanently is 36,274. This figure was around 31,000 in May.