If I recall correctly, people have found mushrooms that were dried over 100 years ago that were still just as potent as they were originally. Psilocybin doesn't seem to degrade over time.
Shrooms will last for years if dried and stored out of the light and kept dry. I have left them in my safe wrapped in a ziplock and found that even after 18+ months they were as punchi as when first time I got em. Nothing extra special like a fridge or freezer, just a cool dark dry storage.:devil: