I currently have two bottles of cologne - one I’m trying to use up. It is stuff I wore in my early 20s and Mom bought it for me for XMas a few years ago, thinking I still like it. I don’t hate it, but would not wear it otherwise. In any case, both are a few years old.
Dark is supposed to be particularly critical. I have a bottle I bought that’s been around for seven years with no apparent change. My husband bought me a vintage Channel that’s quite a bit older than that. I can’t say that it hasn’t changed, but I can’t detect anything off.
I would test a questionable perfume, and also get a second opinion. There’s nothing worse than a rancid or ‘off’ perfume! I have an almost full bottle of Yardley April Violets that turned :(, it must be older than I thought, and I don’t think they make it any more. But I have a Dior perfume, much much older, and it smells as divine today as it did when I bought it. I think it depends on what it’s made of - the violet perfume is mainly chemicals as there is no way to extract the scent from actual violets. The Dior perfume is so old that actual flower extracts were used in making it.