I know there are a lot of thread on shelf life for face make up but I couldn't find one on nail polish. I'm going through and organizing my nail polishes. I'm finding that I have some bottles that are over 10-15 years old. Obviously, if the nail polish is thick or goopy, it is time to toss them. But what about the ones that are thin and rarely used, and look ok. The color has separated on some, but when I shake it up, it looks fine. Is there anything wrong with using really old nail polish or is it time to toss these too?