Maybe it's a climate thing, but so far, mold hasn't been much of an issue, and nothing I've jarred so far has developed mold. SoCal has a dry climate. Also, I sterilize all surfaces before I start jarring, so perhaps that helps as well. But mold spores are everywhere, including the factories in which tobacco is blended and tinned.
That's terrible news about the Haddo's, but also interesting since it was tinned by C&D, who have had more issues with mold than any other single maker.
Generally, the canister type tins hold up just fine for decades. I know a couple of long term McClelland heads who are still opening the occasional tin that they bought in the 1970's and '80's with the contents still preserved.
The pressure, or friction, seal tins are more hit or miss, with the square and rectangular tins being worse than the round tins because the seal pressure around the perimeter isn't consistent. Keep in mind that many, if not most, of these tins are very slowly leaking from the get go. They'll mostly do well for 5 or more years, then become more hit or miss over the long haul. So the question of whether ultimately to jar or not depends on how long you plan to age or store your stash. And you can always vacuum seal the jar to slow down aging. Aging changes tobacco blends, but it doesn't always improve them.
Widespread cellaring is a fairly recent phenomenon, maybe the past 20+ years or so. Aging tobaccos for decades is more of a recent thing. In the past long term aging was mostly chance, not a deliberate strategy. Tobaccos were well aged before they made it to the tobacconist's shelves. We just bought a tin or two of what we wanted and didn't worry about amassing a treasure trove. Most of these tins were made to hold up "long enough". They weren't intended to be good for a decade or more, so don't be surprised if you open a tin and occasionally find dried out contents. And if worse comes to worse, you can always rehydrate, though you cannot resurrect.
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