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Can a house or estate that fulfilled one City Plan count toward another City Plan?
The rulebook states the rule and the designer repeated it several times.
No, not for plans that target houses or estates. When you claim such a plan, draw a line above the houses used; they cannot satisfy another plan, and the estate cannot be subdivided with a Surveyor fence either (even if zombies later split it). The estate still scores normally at the end of the game.