how long does nail varnish last?!

[ChickenNuggetLover]

Just doing my some nails, and the one I'm using us about four years old. It doesn't seem to me drying.... Do they actually stop working?! No logo on it showing shelf life either....

In my experience it gets gloopy after a while of use. Maybe the reason it's taking long to dry is because it's thick? But it depends on the brand, what make are you using, and how many coats you have put on.

It was No.7 and I was doing a couple of coats. Not sure whether to bin any varnish older than a couple of years?