According to the "Sterbebücher" (death records) of Auschwitz, Leonard Sanders was murdered there on 29 December 1942. This date differs from the official date of death of 28 February 1943, 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 "Nederlandse Staatscourant" (Dutch Government Gazette) by the Ministry of Justice.
Date of death as in the Sterbebücher Auschwitz (death record)
The official death certificate no. 125 dated 14 December 1950, made out in Amsterdam for Leonard Sanders. (after clicking wait a few seconds till the register opens).