According to the "Totenbuch” – Death Records of Auschwitz III (Monowitz), Louis de Haan was murdered there on 15 May 1944. This date is a slightly different from the official date of death of 16 May 1944, 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.
Officiële overlijdensakte nr. 462 voor Louis de Haan van 22 Februari 1952 uit Amsterdam
Other sources from the website Memorial & Museum Auschwitz-Birkenau/Auschwitz Prisoners:
1. Häftlingskrankenbau Auschwitz III
2. Häftlingskrankenbau Auschwitz III - Totenbuch