Well it's certainly true that different yeast will produce different profiles of the congeners, the things that produce flavor (good and bad), as well as headaches in excess quantities.
Certainly lead is another possible source of bad stuff leading to a short life span. I don't think there are single answers, and the late 18th century probably had a number of sources. But not all stills were made with solder. I have a still from Portugal that simply riveted. And apparently this was a very traditional still construction. And it didn't leak vapor until I dropped it into the sink one day by accident. Now it's all silver soldered.
Verdigris is the green on copper, like when exposed to the sea. It was used for a pigment in oil paints for many years. But it's not something you want to eat or ingest. The reason I asked about this, is I have all copper stills and I've never had this green on the inside of my stills, nor have I seen any discolored distillate. But a couple of these old books definitely talk about this as a real problem. So the question becomes, why? Why does it happen? Under what conditions? We won't ever know if it was a common problem unless someone finds the forgotten cache of the Old Dr. Crow's Whiskey Museum.
The way alcohol and whiskey has been demonized leads me to think that maybe there was something other than just whiskey in the bottles (or barrels/jugs) in the early days. That's certainly true for absinthe. It was totally demonized and yet actual GC/MS analysis of old pre-Ban absinthe shows nothing dangerous. (These were samples of good brands, not of the cheap stuff came down to us.)
I'm not as up on my yeast microbiology as I should be, but all the ones used in making spirits and wine work as Lavoisier described, by converting sugar into 99.9% ethanol and CO2. I think what they called a "bad ferment" probably was from something other than yeast (remember they didn't know of bacteria or fungi back then). A Lactobacillus perhaps. Normally your wouldn't think to distill something that had been fermented by C. butrysis (spellings wrong, but it producing vomit aroma in a big way). That's my guess. But maybe Mike can point me to some specific yeasts that produce methanol rather than ethanol. I think some bacteria are used to produce methanol and acetone; read that somewhere recently. But they certainly couldn't be common.
Sometimes yeast is fine, but if you give it poor living conditions it's going to produce more undesirable congeners. But still not in large quantities. Because if it's still not producing much alcohol, when you run it you're not going to get much out. It'll be mostly water, or your yield will be really low. But they expected low yields back then.
I think you may be right Mike that the fellow made some dangerous whiskey. But the folks drank plenty enough of it.
Any way of finding out the cemetery where their buried, or maybe how long they lived, maybe from some church records? Did these folks move from the East to KY? If so, maybe there's some birth records. Did these people die over long periods of time? Or all close together in time?
btw, are there other records like this, of people dying from poison whiskey? I mean real documented events. I know in modern times you read about it but it's always from someone adding something to the spirit, not from the ferment.
If it was just heads and tails, distilling would be much more regulated, and even our whiskies would have to be analyzed. But US distillers aren't even required to to submit a formula for whiskey let alone a lab analysis.
Sorry if I'm just showing how poorly read I am. It wouldn't be the first time!