A couple of topics in the responses are interesting and worth addressing.
First is the amount of air to tobacco in tins or jars. When one takes a moment to look at how commercial tins are packed and sealed it's clear that from the commercial standpoint it doesn't matter. Hearth & Home tins used to be tightly packed and vacuum sealed, whereas McClelland tins had loose packing and plenty of air in the tin. C&D, GL Pease canister tins aren't hard packed with no air. HU and Peretti paint can tins, loose pack and no vacuum. Either commercial blenders don't give a crap how their blends cellar, are flagrantly incompetent, or it doesn't matter.
So what do you think? Are commercial blenders incompetent, don't give a crap, or does it probably not matter. Also, the quality blenders do their own aging BEFORE blends are released, so you really don't need to be further aging them as far as the blenders are concerned.
Second is the matter of square and rectangular tin seals. These are sealed with a gasket that's never 100% sealed. There's always a tiny amount of leakage, which is why you can smell the contents if you put a tin in a sealed Rubbermaid container for a couple of weeks, lift the lid, and take a sniff. This is why your closets, basement, display case, or underwear drawer, stink of tobacco. These square and rectangular tins use a gasket seal, and as anyone with even a smattering of engineering knowledge knows, the distributed pressure is concentrated in the corners and less so in the centers of the sides, so uneven pressure along the perimeter of the seal. That's not the case with circular screw down lids. Granted, ANY seal can fail, but in my personal experience, seals on rectangular and square tins fail sooner and in higher percentages. So it comes down to how long do you contemplate your tins will have to hold up? A decade or less? You'll probably mostly be OK. Some of your tins will die in glorious service to you, but most will be OK, just as long as you keep storage temperature variations marginal. Longer than that? Consult a soothsayer.