Hall in Tirol, Austria, 27 Jun 1911, to Diekirch
Here a five-centime Arms postal card has been “converted” to a reply (Rückantwort) card, and has also been properly uprated to the UPU rate with a five-centime Arms definitive.
Years ago, we often enclosed an addressed return envelope or postal card as a courtesy to our correspondent. Perhaps that is the explanation for this postal stationery curiosity.
I base my inference on the fact that the handwriting on the front and back does not match. This suggests that the card was already addressed when the Austrian sender received it (presumably to post a reply).
Sadly, the card has been poorly preserved. Nonetheless, it’s a keeper, possibly unique.