Thanks again for all the advice, friends. Discovered the problem with the Presbyterian was that a Bengal Slices ghost was indeed changing the flavor profile of the former, and I was puffing too hard in my attempt to get the expected Presbyterian brightness, resulting in a hot, foul smoke. A bit of cleaning, careful packing and patience resolved the issue.
The Black House, on the other hand, really has lost its flavor. A shame, because it’s my favorite smoke. I’ll have to be more diligent about keeping it fresh next time I crack a tin.
One thing I don’t quite understand: how does a tobacco lose its oils? I’ve smoked bone-dry tobacco before and it’s still been flavorful - for instance, if I take fresh tobacco from a jar and dry it to a crisp under a lamp, usually it still tastes right. But this Black House is deader than a doornail. Too much air exposure or something?