Tins are good indefinitely, provided that there is no rust or denting that may have broken the seal. Coin-twist lids (the shoe-polish style tins) are, IMHO, slightly more susceptible to the elements; a properly sealed tin will evidence no shaking of the contents. Rust spots can indicate a compromised seal, even from nearly microscopic holes. For your own storage, if you're intending to cellar for many years, make sure you've got an environment that's low humidity and cool & dark. There is no need to jar tins, save the mason jars for your bulk purchases.