There have been a lot of threads about how long unmixed epoxy lasts, before "goes bad", and I think this may help answer that question.
I just completed one have of a two part POP mold, and wanted to seal it with epoxy before I poured the second part.
I had some Etex up on a shelf in my garage that was more than ten years old. It has been through temps from low 30's to 100's over the years.
I haven't used it in at least five years, but I decided to see if it was still good.
The catalyst was still liquid, but the resin had turned solid for the most part. There was still a bit of liquid resin left, so I drained it into a salsa cup, added the same volume of the catalyst, mixed it very thoroughly, and then added another 25% denatured alcohol to thin it.
I brushed the mix onto the dried/cured POP mold half, wetting it completely, and left it to cure overnight.
When I checked it this morning it had cured out hard, clear, and shiny, and I'm going to go down this afternoon and pour the second half ove the mold.
I had to chuck the resin bottle, since all that was left was hardened resin, but it showed me that, as long as the resin is liquid, it is good to use, at least for sealing POP.