In my experience, access to medical records differs from state to state and many records are only kept for a certain period of time. If the informant is listed as the records of the facility, it would appear that the data found on the death cert was provided by the hospital. So, that data may be only as good as the info the hospital received at the time of admission. I have found residents of such facilities in Census records if that is of any use. There is some decent info on the facility (apparently still in use) here.
it says that they have annual reports 1882-1959 but I can't find them and there are 47 volumes http://www.phmc.state.pa.us/bah/aaGuide/AA-RG-23.html
There's a Norristown State Hospital Historical Association - https://www.facebook.com/NorristownStateHospitalHistoricalSociety/. I doubt that the have records, but I bet they know where the records are.
