I do not believe in nail polish expiration dates. Microbes typically cannot survive in polish, and the period after opening number on some nail polish bottles is merely a formality. They are there for governments or consumers who like them. Surely there are exceptions, but polishes that are well taken care of generally last a long time. Store them away from heat and light, and make sure you close them as tightly as possible after each use. Keeping air from penetrating the bottles is key. Bottles that are not tightly closed will go bad quickly, even if they’re brand new. Over time, some polishes break down faster than others. The brands I am mentioning in this article are guilty of this. Before tossing polish, it is always a good idea to attempt restoration. If your polish is so hard that you cannot pull the brush out, restoration gets a lot more difficult. Tossing those is probably best, although not necessary.