Mexico. 1934 (Sept.) National University, Air 20c. to 20p. set of eight in unmounted mint blocks of four; some gum toning on low values. A rare set in multiples, seldom offered. S.G. 553-560, £5,600 (Image1)

Est. £1,000-1,500

Mexico. 1935 (Apr.) Air, Amelia Earhart 20c. lake, large part original gum, fine. Only 480 examples printed. A key stamp of Mexico and an Air Mail rarity. P.F. Certificate (1972). S.G. 581a, £3,500. (Image1)

Est. £600-900

Mexico. 1939 Air, Sarabia 20c. blue and red unmounted mint block of four from the upper corner of the sheet, fine and rare. S.G. 626a, £1,900+ (Image1)

Est. £300-500

Mexico. 1935 Air Amelia Earhart 20c. lake, from the bottom left of the sheet, unmounted with a few toned perfs and natural paper bends; otherwise a an impressive example of this scarce and important stamp. Friedl Certificate (1957). S.G. 581a, £3,500 (Image1)

Est. £500-700

Mexico. 1939 Air Sarabia 20c. blue and red right-hand marginal example, fine unmounted mint. S.G. 626a, £475 (Image1)

Est. £100-150