From the certificate of death no. 105, made out on 20 December 1944, is appears that Herman Kattenburg has been found dead on 16 December 1944. Which means that he might have died earlier, but only is discovered on 16 December. The real date of death, as well the date of death of his spouse, appeared to be 26 November 1944, as a result of the bombardment on the Euterpestraat in Amsterdam.
The website Joods Monument only publishes the formal and legal date of death, in accordance with the official death certificate drawn up at the time. Which is for Herman Kattenburg and his wife 16 December 1944. However, in an additional text the actual date of death can then be explained and stated and why there is a difference.
Source: City Archive of Amsterdam, certificate of death no.105 dated 20 December 1944, year 1944, register 15-folio 18verso for Herman Kattenburg and deathf certificate no.117 dated 21 December 1944, year 1944, register 16-folio 20 verso for Sijbrigje Rosier.