An inquiry into failings at Shrewsbury and Telford Hospital Trust (SaTH) had initially focused on 23 cases, but more than 600 are now being looked at.
It comes as the NHS revealed more than 326 new cases of concern, some from 1998, but families have not been told.
The trust will now contact affected families.
An interim report from the continuing inquiry, leaked to The Independent earlier this week, described how children were also left disabled during their time at the maternity unit, where staff got the names of some dead babies wrong.
The review, which covers as far back as 1979, is being led by maternity expert Donna Ockenden.
A letter from NHS Improvement’s National Medical Director Prof Steve Powis, to families in July 2019, says it identified a further 326 from its search, which was begun in September 2018, and would be working with the inquiry for “appropriate cases” to be included.
But four months later, it had not yet contacted those families to inform them their cases had been identified and to ask permission for them to be included in the inquiry.