Lot 626, Canada 1938 six cent blue Monoplane airmail plate proof pair, sold for C$374 July 24, 2020November 15, 2018 by Sparks Auctions Lot 626 Canada #C6P 1938 6c blue Monoplane over Mackenzie River Plate Proof, a vertical pair from left side of sheet, printed on card-mounted India paper, very fine. Unitrade CV$400, sold for C$325.00 plus 15% buyer’s premium.