It depends. (You knew that was gonna happen...)
For organic liquids the manufacturers usually state they only have a shelf life of about 90 days. For everything else - at least one year.
Storage helps. Keep the stuff you aren't using in a cool, dry environment out of direct light. Refrigeration usually isn't a good idea. Plastic bottles or even glass bottles - with rubber stoppers - will do flavor transfer if stored long term in a fridge. I don't want my Chai Tea
vape tasting of an onion undertone.