I had about two oz. of seeds from the early 1970s (mostly 71/72) in a large steel Peanut can with fitting plastic lid. Stored indoors in the bottom dresser drawer. They were still Viable at 17-18 years, with about a 50% germination rate. I was not growing nor smoking during this time frame, but when I tried them again in 2012 or so, none germinated out of thousands. None of them came from "exceptional" weed, though - all were from $10 Lids of Mexican pot, so no big loss. Based on this experience, I tell people that - aside from any exceptional Storage methods (which I did not take), seeds generally last "about 20 years". If someone were to use more sophisticated Storage methods (not common), they might push that "20" out a bit further....but not much.
Yes, I've heard of seeds from ancient Egyptian tombs still being viable at 3,000 years....but we're not Scientists. Just normal people.