I have used various epoxies that have been 2 or 3 years old. No problems catylalizing have appeared. One observation that I have made with WEST 205,206 and 207 hardner is that over time they will darken in color. Somwhere in the WEST product info I remember reading that this is normal and will not affect its strength. On my most recent boat I switched from WEST to MAS. I had some old WEST 105 resin and 207 hardner that I didn't want to waste and used it in areas where color was not important(ie.inside of deck). My guess is that there are several factors that will effect shelf life such as temperature, moisture etc. MAS may be conservative in their claims. I am sure a call to their customer service dept. would clarify some of this.

Ken