I've kept this as more of a curiosity than anything else.
In the day, one would write to the Post Office where a new postal card was issued and ask for a first day cancel, enclosing the proper remittance and a self addressed stamped envelope for a cleanly returned postal card.
In this case, I was writing for a 10c Salt Lake Temple Postcard. The curiosity is that the return envelope was postmarked with the first day cancellation for that postcard but on stamps unrelated to the first day cancel.
I suppose there is a postal regulation that prohibits this, but it was probably more of a postal clerk wanting to please a stamp collector.
Nothing of particular value, I know, but I do find these sort of cancellations quite interesting.
