Scottish (and most, although not all, other types of) whisky is produced using a "pot still" rather than a modern column, so you don't get an exact separation b

Scottish (and most, although not all, other types of) whisky is produced using a "pot still" rather than a modern column, so you don't get an exact separation by boiling points. I mean, generally you're running the still at under 100C, but you get a substantial fraction of water (~30%) in the output as well. I suspect that if you plotted the still's throughput as a function of boiling point of the inputs, what you'd get is a fairly broad normal distribution centered on the temperature of the still "head" during the distillation run, with the width of the curve dependent on the design of the still. The upper tail of that curve could easily (must, really) be catching small amounts of substances that boil at 200+C.