I did not know this

Have you ever wondered about the shelf life of your cosmetics? We know they don't work when they get old (much like a lot of us humans) but when is that?
Turn over the cosmetic container and on the bottom or side you will see a symbol of an open jar and on it is (e.g.) 24m or 6m denoting the number of months your product will stay fresh once opened.
How clever.
It's up to you to remember when you opened the jar.