O10 (O10) 1910 ½d green Britannia overprinted "OFFICIAL" SG Type O2 on ordinary paper, wmkd MCA, perf 14, block of 12 (2 x 6), by far the largest existing used multiple, very scarce and undercatalogued, ex-Tyrrell, ex-Ramkissoon's Gold Medal collection, with Sismondo certificate for the block of 18 that is from.
