Rehd,
The first boat I built was a CLC kit that sat around for 2 1/2 years before I had the time and space to build it. I was a little worried about the MAS hardener as it claimed to have an "expiration date" of one year. I contacted MAS and they told me they have old (10 year +) epoxy that they periodically mix up to test and have never had a problem. The purpose of the exp. date (according to MAS) is that the hardener darkens becoming less clear, which mine did. However once applied on the boat it was not noticeable (no "clear" on the same boat to compare it to) and I've had no problems 4 years latter.

David