According to the "Sterbebücher" (death records) of Auschwitz, Ruben Heertje was murdered on 27 August 1942. This date is different from the official date of death as determined by the Dutch Ministry of Justice after the war. For the time being, the website joodsmonument.nl, list only the dates of death, as published at the time in the “Staatscourant” by the Ministry of Justice.
Auschwitz death record for Ruben Heertje (Sterbebuch)
The official Dutch certificate of death nr. 347 of 4 Aug 1950 from the A-register 44-folio 59v.