Yes. Fragrance can slowly fade during storage, especially if wax melts are exposed to heat, sunlight, or open air for long periods. That does not mean a melt suddenly expires on a particular date, but very old or poorly stored melts may not smell as strong as they did when fresh.
Keep unused wax melts sealed or closed in their original packaging and store them somewhere cool, dry, and away from direct sunlight. Avoid leaving them in a hot vehicle or next to a sunny window. Good storage helps protect both the fragrance and the physical condition of the wax.