I don't drink much hard liquor at all, for no particular reason. But, years ago, I did establish a little bar in my wall unit. I have bottles of scotch, rye and a few other things, unopened, for at least 10 years. My joke is that the 12 year old scotch is now twice that, at least.
Then there's the open vodka, dark rum, light rum, amaretto, frangelico, brandy, grand marnier and framboise that I do drink and cook/bake with, but which I have had for quite awhile also, some maybe a couple of years. How can I tell if this is still usable, even for cooking/baking?