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 K - Rayado vertical of English origin, a parallel watermark with an asymmetrical paper mesh! And coated of course! Assigned watermark type I so it must be like the uncoated version "F". First use in 1949 although the reference for commemorative stamps suggest differently: 
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 The 12.10.1947 400 year Cervantes stamps have both K and JC! Cervantes with both the parallel and the orthogonal watermarks!! All having an asymmetrical paper mesh... All in photogravure! Parallel: 
 Orthogonal: 
 
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