Netherlands, Stamp Day Amsterdam 11 October 1942 registered air mail > HAMBURG

    The four values removed by Geman forces from the government printing works and distributed through the German philatelic trade.
Never issued for postage.
These 4 copies with No 14 in margin are each canelled by special stamp day c.d.s.
A regular 12 1/2c air mail stampcbelow appears to be the sole adhesive not cancelled. it, in fact, overlaps the lower special cancellation.

Almost certainly applied spuriously to give some credibility to the missive.
All the same - a most attractive little oddity of invalid stamps seemingly doing genuine  postal service.