The content of these "certificates of change of death data" means:
In 1949 has been recorded in his certificate of death that Karl Heinz Pfeffer has been killed 28 February 1945 in Mid Europe but 21 June 1957 the District Court of Amsterdam ordered the change of date of death in the registers of death of the Civil Registry of Amsterdam into "7 July 1944". (cert. nr. 19).
And
The District Court of Amsterdam ordered 21 June 1957 the change of date of death for Henriette de Leeuw, Jan Peter Pfeffer and Thomas Pfeffer from “about July 1944” into “7 July 1944” (cert. nr. 20).
Source: https://archief.amsterdam/inventarissen/inventaris/5009.nl.html#A13064000079