... AFAIK comercial UV-curing photo-polymers are specified with 3 to max. 6 months storage time for their resins.
I have some test samples and a half full 1kg-bottle of UV-resin from spot-a from my first tests maybe 4 years ago ... so thought, it's all not usable anymore.
For tests with paste-jetting I was searching UV-curing colours and resins and remembered and found the samples, stored in a dark edge in a card-box in the basement.
One of the small samples is hardened to a sort of wax ... the other sample is pretty high viscous, darker yellow than when new, but fluid and reacting to UV with exothermic reaction, so could be usable.
But the resin in the 1kg-bottle is clear and low viscous like new, and reacting too with a 405nm-LED after 4 years!!
Will test mixing some acrylic colour to the resins and paste-jetting some samples for front panels and maybe some "ink-jet-3D-printing" too the next weeks ...