All Yeti Labs solvent-free epoxies have essentially unlimited shelf lives so long as they are stored in sealed containers. The resin may crystallize or the hardener may darken but this does not affect its performance. If the material is more than a year old do a test to satisfy yourself that it cures properly. We recommend 24 months as a universal shelf life for our products, although we also recommend using the product within a few months prior to any possible material changes.
The hardener oxidizes from oxygen which can discolor it slowly while stored over time. Sometimes the user believes it is not good (hence throwing away). Reality is the material may still be good, but just does not look the same.
As always, please test a small amount prior to any large installations.