I've had the same bottle of Bunnhabhain 12 in 175ml airline-wine-bottles, and one was open since Spring, and the other I opened tonight.
To address the question about whether whiskies change when open: yes, they are different.
To qualify that--neither of these two are in the league of the Bunnahabhain
12 I bought about two years ago, when it was reputed that they were using 18-year-old stock for the 12 year old.These 2 bunnies from the same bottle are worthwhile, but not the deep, rich, meister-klasse of that earlier Bun, which was all sorts of mellowness and depth.
The one of the two from the same bottle open since Spring is better. Time sucking up air has helped this dram. It is gentler, warmer, and has a maply edge to the pleasant caramel, whereas the newly opened 175ml bottle is spirity and almost raspy. Neither are anywhere near as good as my Bunny bottle from two years bac, but the newer bottle has a touch of pleasant caramel but the older one has a dimension that the fresh opening does not have: "dresser drawer".
I realize that "dresser drawer" is not common parlance in tasting-note circles, but it is meant to suggest a touch of old cedar wood that goes beyond the basic burst of burn that the new one has. I assume you are all understanding perfectly well what I am saying. Or are at least ewhat I am pretending to saying.
Because that is the language of tasting notes. Tasting notes talk about "cedar box engraved with Daniel Boone signature embossment with fig, apricot, and Toy-Story figurine lickings". NO they don't. They leave OUT the 'Daniel Boone' and the 'Toy Story figurine licking' bits, because, let's be frank, they only mention things that you can pick up at the Saturday market at Aix-en-Provence. That's because the things you can pick up at the Saturday market at Aix-en-Provence sound classy, and the other things the nose can actually perceive clearly DON'T.
But let's be honest. Sometimes you can pick up essences of carburetor, essences of swamp gas, essences of formaldehyde--but nobody mentions them. Why?
You know why.
In any case, the Bunny open to air since spring is better than the Bunny from the same bottle I just unleashed.