Around 1,500 more patients of convicted breast surgeon Ian Paterson are being recalled by health officials so their treatment can be investigated.
Spire Healthcare, which runs private hospitals, announced the move after revisiting "historic legacy IT systems" which had been thought to be "inaccessible".
Solicitors who have represented hundreds of Paterson's clients asked how so many people had been missed off earlier recalls "due to a computer glitch".
Paterson was jailed for 20 years in 2017 for 17 counts of wounding people with intent.
He subjected more than 1,000 patients to unnecessary and damaging operations over 14 years.
A 2020 independent inquiry ruled he was free to perform harmful surgery in NHS and private hospitals because of "a culture of avoidance and denial".
The inquiry said all 11,000 patients Paterson treated should be recalled for review.
Between 1997 and 2011, Paterson is known to have treated thousands of patients at Spire Parkway hospital and Spire Little Aston hospital in the West Midlands.
This was alongside his work at NHS hospitals run by the Heart of England NHS Foundation Trust.
In a statement, Spire said further checks were carried out to be "certain that there were no outstanding patients who might require support, dating back to the earliest years of his practice".
It added: "To do this, (Spire) revisited historic legacy IT systems, in use between 1993 and the early 2000s, containing information about patients from over 20 years ago which had been thought to be inaccessible.
"However, following a further complex analysis of these legacy systems, Spire was able to identify the details of around 1,500 patients."
Dr Cathy Cale, Spire's group medical director, said: "We are very sorry for the significant distress and harm suffered by patients who were treated by Ian Paterson.
"We accepted the recommendations of the independent inquiry into Paterson in 2020 and are fully committed to implementing them."
'Recall will bring back bitter memories'
Linda Millband, head of clinical negligence at Thompsons Solicitors, which has represented hundreds of Paterson's clients, said: "The fact that 1,500 patients could have been missed off both previous recalls shows how extensively Spire enabled Paterson to practice.
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"For patients who have suffered from his negligence and for those who have lost loved ones, this recall will bring back bitter memories. For those being alerted for the first time there will be shock and worry.
"You would have thought that after two recalls Spire would not have left any stone unturned, yet they missed at least 1,500 people due to a computer glitch. It begs the question - 'what next'?"
Spire said anyone concerned about treatment from Paterson should call its freephone helpline on 0800 085 8130 or visit spirehealthcare.com.