63a (B11a) 1915 2' on 2M blue Kaiser's Yacht overprinted "C.E.F.", VARIETY - "S" inverted, only 100 printed, in practice only a trivial percentage of mark values were used, as such seriously undercatalogued, left-hand sheet-margin example with "Duala * b" cds, in our 40 years this is only the third example we have encountered, a great used rarity.
