Saving matza from the afikomen is a shmira [protection] for the home. Is the matza saved from last year chametz the following year? If yes, if the matza from last year was discovered on pesach what should be done with it?
As long as the Matza was kept in a sealed bag, away from chametz, it remains kosher for Pesach, even a year later.
Once matza has been baked it no longer rises and can no longer become chametz. This is what makes “matzo meal” permissible for use. There is no time limitation on this.