Jacob Elias Koster was the son of Victor Koster and Roosje de Kromme. He married to Saartje Les, daughter of Philip Les and Jetje Baks, on 6th February 1924 in Amsterdam.
Addition of a visitor of the website
In addition, a Jokos file (number 50776) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.