More than 20 Life Esidimeni patients are still unaccounted for.
In a statement on Sunday, DA MP Jack Bloom said police had informed him that 28 patients were still missing.
The Gauteng health department has, however, disputed this, with spokesperson Lesemang Matuka saying the actual figure is 22.
The police could not be reached for comment.
Bloom said the figures followed the missing persons case he had opened with police earlier this year.
"While I am pleased that the original list of 62 has been reduced to 28 patients, there is a decreasing chance of finding them all since they were discharged two years ago from Esidimeni to illegally registered NGOs."
Bloom said that based on the list he was given by police, 18 men and 10 women, with ages ranging from 27 to 79, were missing.
"In two cases the date of birth is given as 1900 and 1914 but this seems to be a mistake," he said.
Bloom said that three people were not named on the list, with one having the description: "Male child David".
"It is distressing that so many patients have still not been found, which highlights the fact that the Esidimeni tragedy is still not over," said Bloom.
At least 144 psychiatric patients died in 2016 after the Gauteng department of health moved 1 700 mentally ill people from Life Esidimeni homes into ill-equipped NGOs and state facilities.