The lowest datalevel pgc have for caches places all caches in the all areas in Stade (Lkr). So it is a smaller division that is needed. It can be done but reliable border polygons are needed. Does the areas needed in the challenge exit on opensteetmap with correct borders or are there another source of the borders.
If the polygon exist a checker can be created.
But i cant determine that with my limited knowlage of the area.