Oh John Hansell's blog
, he discusses how the Sazerac 18-year old rye is different in each of three vintages. The first year's rye was from a different set of barrels, but the second two releases are the same batch of whiskey stored a year in stainless steel. According to the information sent to him, the only difference was that the whiskey sat in the tanks- with a large area exposed to oxygen- for a year. The difference between the two years is due to oxidation.
That's all fine and interesting on its own, but should also act as a reminder that whiskey can change even when not in wood if the bottle is empty enough, so I should most likely start finishing the dregs of a 25-year-old Macallan that's been sitting quietly in my cupboard for too long.