Late 50s or early 60s would seem to make sense then. I just figured there must be a connection to the stamps it refers too and if you found a mention of stamps from the 50s/60s period, there you go. Since there's not much from Thorpe's football playing days, surprised these have gone so unnoticed even being from after his passing and European. Considering the 1955 Topps All American card of Thorpe is rather desirable maybe this card, whatever it is, is comparable to the Bond Bread Jackie Robinson. Just had to throw a Bond Bread shout out in there.
Either way, cool looking cards with bold images and seemingly rare!