South Africa 1975 4c Pres Diederichs Black Jacket, 60 Possible

1975 Inauguration of State President Diederichs: 4c (SG 376var/CC 381var). Complete vertical strip of five, marginal top & bottom, the fourth stamp showing so-called "BLACK JACKET" variety. Three sheets (of 100) were found to each contain a row of affected stamps where the stamps appear black rather than brown... ie only sixty copies of the error can exist. Variety probably due to interrupted printing. Rare, a much-underrated Republic error.