Sc.C1 + C2, 1925 5c. blue with "AEREO - CORREO" overprint in black and blue, VF quality, rare, with guarantee marks of Sanabria, catalog value US$387. (Image)

Sc.C21 + C24, 1930 5c. on 10c. with YELLOW overprint + 10c. on 20c., VIOLET overprint, mint and of very fine quality, rare, both signed by Alberto Diena, catalog value US$1,200. (Image)