Research into the wartime civil registries of one of the civil registry offices in Upper Silesias (Poland) discovered many records that corresponded to deaths of inmates from the "Reichsautobahnlager Annaburg" and "Zwangsarbeitslager Niederkirch" camps.
A certificate of death for Isidorus Schijvenschuurder as discovered there, stated that he died on 29 November 1942 in Camp Annaberg. In it was mentioned an official cause of death as “heart failure” (Herzschwäche).
The archives of the Jewish Council of Amsterdam list Isidorus Schijvenschuurder being deported from Camp Westerbork "eastward" on 2 October 1942.
Private collection of Edward Haduch, Kedzierzyn-Kozle (Poland), the official death certificate of Isidorus Schijvenschuurder, issued by German authorities (Standesamt) of Annaberg and the Archive of the Jewish Council of Amsterdam.
However, by establishing the date of death of Isidorus Schijvenschuurder, the official date is maintained as stated after the war by the Dutch Department of Justice.