For what it's worth, G&H have said before that their blends are designed to be enjoyed fresh and not meant for aging. I have several of their tins unopened that I haven't gotten to yet, but Ennerdale didn't hold up after 2 or 3 months, or maybe 6 months, I don't remember (I had forgotten about it and came upon the open tin later, and I don't now remember how long it had been opened when I found it again).
I have noticed some aros definitely loose a lot of their luster at the 1-2 month mark, while others seem to not change much at all even 6 months later. People knock PG, but damn if it doesn't help that flavor last.
But it should be noted, I don't jar/seal my tobaccos. Once they're opened, they go in an air-tight food storage container with other open tins in the same genre, and I keep my tobacco in the tin it comes in, but despite being air tight, there's still air in there (not vacuum sealed). It's also why I typically get small tins (50 g/1.75 oz), and try not to have too many open at once. A small tin usually lasts me a month if I smoke one bowl per day out of it. I do keep them in a cabinet though (no sunlight), but it's also not a cool place (just room temperature).
But, even if you vacuum seal the tobacco after you pop the tin, you've already restarted some fermentation with that little bit of air it was exposed to, and it doesn't immediately stop once you seal it.