This person lived alone or no information about family members is known or traceable.
The date mentioned here is the legal date of death of Abraham den Hartog maintained by Dutch Ministry of Justice. In the City Archive of Rotterdam there is a certificate of death of Abraham den Hartog that has 20 September 1942 as the date of death.
Source: City Archive of Rotterdam, page v4-027 date 1950
In addition, a Jokos file (number 51957) on this person is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.