When I got my Czechoslovakian air mail stamps which I showed you the other day, they came with the next air mail set down the line.
This set was issued some two years after the previous one, on 15 June 1922. As you can see, the plane itself is rather similar, but the rest of the overprint layout is different. I like the two propellers obliterating the old value! A different kind of stamp was used for the overprints, the "Allegory of Economy and Science" definitives. As far as I know these stamps were not issued for specific flights. They were reprinted in 1970 on thick paper (with facsimile on the back) so do not confuse these with the real thing! Also, forgeries exist, which may be distinguished because the shading of the plane is patchy and the jack (is that the right word for that round thingy on the wings?) is round rather than oval.