Well it's up to you to only introduce correct data... It's better not to map this than it is to not really know but still add it. Anyway, the ones I know about without further research is that Stad Antwerpen only followed in 1983 or so, and here's a list of the 2019 fusions in Flanders: https://www.vlaanderen.be/lokaal-bestuur/samenwerking-fusies-regiovorming-en-verzelfstandiging/gemeentefusies-2014-2019