1936/1937, "VIVA ESPANA / CORREO / AEREO / Orden / 9 Novbre.1936", blue overprint on fiscal stamp 15pts. rose, BLOCK OF FOUR (A0613093+94+98+99), unmounted mint. Rare error of overprint which was designated to be applied on 3pts. value. Very rarely seen, especially as a block of four, stated to be (possibly) unique. Signed M.Galvez/Madrid and certificate Graus. ÷ 1936/1937, 15 pts. rosa, bloque de cuatro. ERROR DE HABILITACION sobre el valor 15 pts. POSSIBLEMENTE UNICO CONOCIDO. Cert. Graus (Image)