I bought a 5 gallon pail say plus 14 years back, never opened kept in the garage though, so a bunch of hot and cold cycles think still good, never opened it.
If you contact the makers of any chemical product, they will give you the "official" shelf life. (unopened original container, proper storage conditions, etc.)
This is the time period where the maker stands behind their product. After this, IF the product does not perform properly, the maker is not responsible.
OFF THE RECORD, most will tell you that if it looks, smells, mixes up, etc., ok, then it will probably work.
14 years? Uncontrolled storage conditions? its anyone's guess. Mix a small test batch and try it on something that is NOT valuable.