The resin will apparently keep for years. If it crystalizes, it can be warmed and then used. However, I understand the hardener may only be good for a year or two. I would suggest mixing up a small quantity and seeing if it cures OK.

Keith (soon to try some that has been open for well over a year!)

A test is good since I have no clue about shelf life of various resin brands and hardener blends, but here in the warm south my fast hardener doesn't get used often and my jug of WEST 205 has turned a deep purple color = still kicks off fine with advertised speed.