Factory sealed tins, usually, are perfect for cellaring as-is. However, three bad things could happen to tins during long term storage. The tin seal could get compromised, and thus result in dried out baccy after years of patient cellaring. Or the tin could catch rust and disentigrate, with the same dried out baccy results. Or the baccy inside could "over-ferment" and make the tin swell to the point of exploding. These bulging tins should be opened (carefully!) immediately and the contents, if not spoiled, transferred to a mason jar to resume their cellaring nap; or consumed expeditiously.

Different kinds of tin seals can be tested in different ways. Square/rectangular tins like Samuel Gawith stock are easy to check. They are basically held together by the vacuum of the seal, when compromised the lid just falls off. A light tug on the lid will quickly reassure the cellaree about the status of its seal. Round pop-off tins such as GL Pease's stock are much stronger in maintaining their sealed state - and it is easier to eyeball the pull-off cap to see if any gaps have opened in the seal/rim. Round screw on tins such as Escudo have probably the sturdiest seals. The only real damage these round tins can suffer is from blunt force impact (typical in snail mail shipping) that could deform the tin shape and pop the seal. Undamaged round tins such as these can also be re-sealed by hand closure during content consumption, remarkable technology.