I jarred many tobaccos, including some tins, lots of bulk and all foil packed bulk. I conclude:
1. some of it ages brilliantly, shows crystals and sometimes even plumes cigar-like;
2. some of it seems to remain static and some improves a little;
3. none is worse for the experience except maybe latakia which often loses intensity*;
4. none if it ever leaks and totally craps out; and
5. johnnyflake probably knows more about this anyone I know. He been around, ya know? He been around.
*not the worst thing if virginia in a latakia blend is also improving.