Is it crusty and lumpy or is the KOH pretty much like it was when you got it? If the former, might have absorbed to water to be worth using. If the latter, I'd use it!
Ditto what DeeAnna said. I just recently used up a bottle of KOH that I bought at least 5 years ago. It was dry and in the same condition as when I bought it, and my soap came out wonderful.