I think it should be valid. Same goes to, when you complete a city, completely surrounded by walls, but with a triangular CCC hole inside, it should be considered completed, according to the "full tile status" of a halfling. (Also meaning, that if somebody later in the game places the fitting CCC inside, he or she can not place a meeple, because the building had been finished and probably, but not necessarily, scored before.) Nevertheless, this might be something, which as well should be officially clarified.