In the Netherlands, a will can only be validly drawn up by notarisation. There are two forms of notarisation: on the one hand, a will can be drawn up directly with the notary (public will), and on the other hand, it can be drawn up privately and merely given to the notary for safekeeping (deposit will).
The notary then enters the will in the register of wills (Centraal Testamenten Register). The register of wills is available at Internet address linked here reachable. Your specialist lawyer for inheritance law in Düsseldorf and Krefeld, Dr Michael Gottschalk, will be happy to answer any questions you may have.