Anniversary Cakes Should Expire or be Retired if Unused
There's a lot of people sitting on inventory of cakes, including myself. There is no point in hoarding these items as we only further contribute to the grind in the game.
I believe that anniversary cakes/flans should expire at the end of the year or close to the next anniversary event so to not go unused.
If you really want to keep it in your inventory, it will still stay but should be put under "Offering No Longer Available"/"This Offering Has Been Retired"