Research uncovered by local history Catherine Corless in 2014, showed there are death certificates for 796 children who died in the Bons Secours Catholic-run home between 1925 and 1961.
A Commission of Inquiry which was established following the emergence of the scandal also found a further 80 children died in the former Galway Central hospital after being admitted from the Tuam home.
Ms Corless could not find any burial records for the children in Tuam and test excavations at the former grounds of the institutions for unmarried mothers in 2016 found a “significant quantity of human remains” in a disused sewage tank.
The country’s first ever mass grave exhumation began at the site on July 14 and is expected to take at least two years.
The requested information on the remainder of the children who died when they were moved from Tuam to Galway hospital and other surrounding hospitals — or were born there as a result of complications in pregnancy.
The Commission's findings show 80 children died in the Galway Central hospital, eight children died in other hospitals and a further 80 died in the Glenadmaddy institution that preceded the Tuam home.
The HSE North West said: “There are no documented process for the burial of babies historically. The only known practice for the burial of babies by the hospital is that they would have been buried in Bothermore Cemetery, in the area known as the Plot of the Angels.
“Regrettably the hospital burial records are incomplete as the significance of this was not fully appreciated until more recent years.”
One of the 80 children who died while in Galway Central hospital is 94-year-old Christina Tully’s son Michael who was stillborn following a complex breech delivery.
Ms Tully, who is from Loughrea, was 18 at the time. She said: “I never saw him, they just said, ‘the baby has died’ and that was it.
“I have prayed for him all my life but I don’t know what happened to him. His father was not the marrying type but I had a second baby with him and he was taken and adopted. I wanted to keep both of the boys."
Patrick Naughton who was born Christopher Tully after his brother and adopted by the nuns, found his mother Ms Tully more than a decade ago and they have tried to locate Michael’s place of burial or whereabouts ever since.
“With all the forced adoptions and the question mark over falsifications of deaths certs Michael could be alive and the closer my mother comes to death the more she has to face two dilemmas — he is either in the mass grave somewhere or adopted illegally," said Mr Naughton.
"It is utterly unacceptable that the hospital has no records for these children."
Ms Tully requested information from Galway hospital about her son’s death but there is only one record in existence that states “return to the Tuam home”.
“That could mean anything, those words have tortured me”, she explained. “And now the hospital says they have no records at all. So where is my child will I ever find out?”