About 2,500 families and more than 800 members of staff contributed to the review, which started in 2022.
But Ockenden said there were “gaps” in knowledge, because some senior leaders declined to engage with her review.
The report said 66 former and current senior colleagues were approached by the chief executive of the trust, of which 37 came forward and 35 were interviewed.
However, experts on the review concluded there were “potentially avoidable” outcomes relating to 444 maternity cases examined up to May 2025, alongside 76 neonatal cases.
All of these 520 cases were graded as two or three for harm, with grade three representing “significant concerns” and grade three “major concerns” over care.
Grade two represents sub-optimal care, in which different management might have made a difference to the outcome, grade three is where different management would reasonably be expected to have made a difference.
The refusal of some management to engage in the review led to the government announcing that the scope of Martha’s Rule would be extended in a bid to boost accountability and safety for mothers and babies.
Other measures include ensuring NHS staff – past and present – who refuse to engage with upcoming maternity reviews are compelled to give evidence, or face up to two years in prison, although it is not yet clear how this will be enforced.