What’s so unusual about this 10c domestic postal card?
The domestic 10c postal card rate was increased to 15c on April 1, 1921. Yet this 10c postal card, which was posted on April 9, 1921, wasn’t taxed. Why?
Well, it has a printed back with no handwriting and is endorsed “Imprimé” [printed matter]. Thus, it qualified for the 3c domestic printed matter rate, resulting in the card actually being overpaid 7c!
Sometimes you can learn more about a card by examining the back rather than the postal markings on the front!