I disagree. I have been preserving mushrooms for over 10 years. I have personally consumed a kilogram over the past year. Early on, when I was inexperienced, I found that they did lose some potency. The reason was not because the loss of potency is inevitable; it was because I did not know how to preserve them correctly. Mushrooms do not become less potent at the year mark. You are preserving them incorrectly.
Assuming they are dried until crisp and kept in a vacuum-sealed container, they will last over two years. I tend to be extra careful with my stash, and check on it periodically. Assuming they remain crisp, like crackers, they are fine. If they start to go even the slightest bit floppy, which doesn't happen to me any more, I will chuck them through the evaporator again. They do not need to be frozen any more than dried fruit needs to be frozen. The trick is to keep moisture out.
I also use home made desiccant pouches, just to be safe. Go to the hardware store and buy a product called damp rid. It's essentially the same stuff they use commercially to preserve various food products. You know those silica gel packets?
No offence, but you're not the authority on the preservation of mushrooms. If you properly dry your stash and keep it in a vacuum-sealed container, with some desiccant pouches, you will not lose potency. Try it and get back to me in a year.