includes unused: 20L32, 20L34, 20L35, 20L36, 20L45 (2), 20L46, and 20L47 block of four; used: 20L32, 20L35 (2), 20L36, 20L43, 20L45 (2), and 20L46; few not counted because of faults, a useful and difficult group, close inspection recommended