Relevant report: After finally pulling some of the American tins from deep in the cellar I transferred several to jars thanks to a wake-up call here. They had a little pinhole rust so were dry but thankfully stored in food saver bags so no loss. I will smoke them as-is. They aren't aging anymore but what the hell, I bought them because I liked them.
Tins from almost 40 years in food saver bags just to keep the ocean salt off of them are mostly fine even though 90% of the bags had failed by now. Interestingly, 99% of the tougher European tins including a couple old-old Escudo and 1980's VA#1 are just fine.
It's the 25 year old tins that have about 75% pinholes, and the failures seem to run in batches. For example, from Pease blends, all Fez are great but Fools Cap and Inverness are dry and Haddo's are 50-50.
Cakes just don't smoke dry well for me and I consider Bengal Slices my only true loss (but haven't given up hope). They are all dry.
As long as there's no mold I'm fine with the dry tobacco, but am experimenting with a drop of PG in a few jars of Inverness and the Bengal Slices. I'll report on those in 10 more years, or one of you youths will when I leave the lot to y'all. Don't go getting any ideas though.