The date mentioned here is the legal date of death as mentioned in the certificate of death of Hartog Koster.
The International Tracing Service at Arolsen has stated in 1990 that Hartog Koster died on 18th of February 1943 at Auschwitz.
Source: Dutch Red Cross, letter International Tracing Service …
We have been unable to determine whether one or more members of this family survived the war. While their names do not appear on the lists of survivors, we have not been able to trace them in In Memoriam either. They are therefore labeled as 'surviving' and their names are not listed.