Les! We've had this discussion amongst ourselves at the pipe club a few times, and I'm still gathering the data. Bear in mind that chemistry is purely a hobby for me, while conjecture and anecdote are my profession.
When opening well-aged blends (let's say anything ten years and above), I have experienced that the flavors *and the moisture* will fade rather more rapidly than newer tins. For example, the 50+ year Escudo that we shared at the picnic was ambrosial upon opening, while a week later it was a mere ghost of itself, and crumbled to dust when packing--and this was sealed in a mason jar. I recently rehydrated some Mel Feldman blends from the early 90s, and while the flavor components were there, the soul of the tobacco seemed to have left. I know this is all rather metaphysical, but there are components to the tasting that I simply don't have the science or vocabulary to quantify. Conversely, a year-old tin of Bedloe's Island I opened up in Kansas CIty a fortnight ago is still vibrant, and perhaps more rounded out, with a bit of airing time.
I got into a heavy discussion with a friend of mine who is extremely knowledgable about wine, trying to pick his brain on this subject. When selecting wines for his own cellar, and at tastings, he will go so far as to aerate a full bottle in a blender. A BLENDER. However, he would never do this to an aged wine; his take was that anything from the cellar should be drunk from the bottle, or perhaps decanted for at most a day--that it should require no more aeration than that. It does make sense as far as the chemistry is concerned: with the addition of air as a carrier, the aromatic volatiles have something to cling to and use as a vehicle for delivery, thus liberating them from the main mass and allowing for some separation when they're applied to our palates. After several bottles and some whisky to boot, which we experimented with by adding water and ice in varying proportion, we came to no further conclusions other than it would be difficult to wake up the next morning.
Tobacco undergoes its fermentation processes differently than a liquid like wine or spirits, though. Exactly how to explicate that, I am again under-qualified to say. The only thing I can rely on here is my own experience, and so far that has shown me that (at least for my tastes) older tins taste best when unsealed, and decline over the next few days with increasing velocity. Another variable, too, is that the excitement of cracking that old tin and reveling in the experience is difficult to prolong due to my lack of patience--and I'm sure that is a huge factor in calibrating my perceptions.