Friction sealed tins, especially the square and rectangular type, rarely form a complete seal. They're slowly leaking from the get go and are pretty hit or miss after 7 years. The round ones would be better since they can distribute the pressure evenly around the perimeter. The canister types seem to do better. But none of these are the equivalent of the old cutter tops. Sealing these friction tins in Mylar may help keep them from drying out when the seal fails, but it's too new a practice to use with any assurance.
The whole notion of widely practiced cellaring is pretty recent, mostly in the last 20 years or so. There were guys out there cellaring before, but they were few and far between. People didn't think about aging tobacco for years on end. Maybe that was because many tobaccos were aged for years and years before they hit the shelves, so they were ready to go when bought. That was the way with the Dunhill manufactured tobaccos. They were aged and fermented before they went out for sale. We just walked into a store and bought a tin of this and a tin of that and it was great.
Most of us are cellaring as a hedge against increases in cost and decreases in availability. But the containers aren't meant to hold up forever. They're "good enough" for "long enough". Your jar is your friend, but even that has its limits as 5 - 10 years on a seal is about it before it needs to be replaced.
And if your tobacco isn't stored in a dark cool location, it may go south in the tin. When you're buying vintage tobaccos on the secondary market, you're often buying tobacco consigned from any number of cellars, and there's no knowing the conditions under which it was cellared. Buying vintage tobacco is a crap shoot because of the many unknowns.
It's great of Pipestud to take care of his customers. But the customer should know that it's not Pipestud's responsibility to do so because vintage tobacco is a gamble that the customer is taking. This really is a caveat emptor market.