Accidents in printing - \"unprinted places\", 13 values with this special feature, on decorative album page with description, including letter with multiple franking 1 Groschen large shield with very prominent large white place, tied by horseshoe cancel \"THORN\" addressed to Leibitsch, those pieces are rare, in the existing number already impressing, partly expertized BPP with four photo attests, (complete photos on the internet)