According to the Death Index (Sterbebücher) of Auschwitz, Benjamin Israël van Polen died there on 7 October 1942. This date appeared to be even later than the official date of death of 30 September 1942 as established after the war by the Dutch Ministery of Justice. For the time being, the website joodsmonument.nl only lists the dates of death, as published at the time in the Dutch State Gazette by the Ministery of Justice.
The date of death of Benjamin Israël van Polen according to the Auschwitz death index (Sterbebuch).
(click the link and wait for opening of the deed in a new window).