Do postage stamps marked 1st Class have an expiry date ? Our local post office is closed and i bought a book of stamps at a shop nearby. I saw they were Xmas stamps and thought they were ok but after I had posted a card I looked on the back of the book and saw the last day of posting for Xmas was 20th Dec....2012 !!@
No. They are fine to use for as long afterwards as you want . with no extra postage needed to be put on with them as long as they have the words first or second class written on them. Postage stamps have been going up every year for some time now and they always go up the end of March.
Christmas stamps can be used all year round, and often are as long as the correct postage is put on.
So long as the stamps make up the correct amount any stamp can be used, even pre-decimal ones. I collect stamps and the supplier recently sent some in an envelope that had stamp's on them from the 1960s.
You paid for them in 2012 with money at 2012 value, no reason they shouldn't remain valid no matter how today's money has been devalued in the meanwhile. Although when they cotton on to the dated gift card con job, they may change their mind.