This regional "employment" of the landzaten was one of the many problems that our republic faced during this war (and other wars). Defence was mostly managed by the States General, but always had to be approved of by the regional/provincial Deputy States, even in small provinces like Utrecht. Each province was an independant state, more or less. Defence lines ran through multiple provinces. And Landzaten from Holland were allowed to serve on Holland territory only. To complicate things: there were Brabant cities that were governed by the province of Holland and therefor had Holland Landzaten on their walls :)
Raymond, returning to my original question: if we were to attempt a non-literal translation of the term landzat/landzaten, in order to express in English the military context in which the term was used, what would be an appropriate word or term.
I have suggested 'local' or 'territorial defence soldier/troops', casting a nod to the Fencibles in C18th Britain, or the 'Local Defence Volunteers' of 1940, although, of course, these were not exact parallels. Perhaps in the light of your comment, 'regional' or 'provincial troops', might express it better- while moving farther from the literal sense of the Nederlandse word.
What does the term landzat communicate to a Netherlander?