Say you hid your LSD blotter wrapped in foil in a book and forgot where you put it and found it 8 years later... it would still be just as good.
It depends on how it was handled before it got to you and how you handle it.
The best thing to do is just keep it in something airtight in a cool dark place. Do not put it in the freezer, it's really easy for moisture to get in and ruin it.