Would you say that there is a noticeable cutoff in quality past a certain number of years, in your experience with aged tobacco?
It's hard to make generalizations because so many unknowns are involved. For example, the conditions under which a tin has sat.
Latakia does fade over time. That's pretty well known and accepted. It's certainly been my experience. Pease, the Dark Lord, has written about it. There will always be exceptions, but so far I haven't experienced any. Latakias seem to hold their potency for 10 to 15 years before starting to "soften" and are mostly gone by, say, 25 to 30 years.
Burleys seem to go on forever. I've tasted clear Burley in an otherwise disgusting 90 year old tin of "oh hell no!".
Virginias go on for decades, but eventually croak out. I've only had a couple of a 60 year old and older tins where the Virginia wasn't a wraith or zombie vomit. Those were extraordinary.
Orientals seem to be long lived and seem to ripen a bit over the years.
Toppings can fade a bit or completely in a couple of decades.
The other problem with really old blends is that they quickly die when exposed to fresh oxygen. The blend might be terrific when opened, only to go flat a day or two later.