I just did a Google search, and this is what it said:
Use Valium within one year
"As a prescription drug, pharmacies limit the use [of Valium] for one year from dispensing,"
I would ask the pharmacist, he/she will possibly know when the date would be, otherwise, throw them away and ask for a new prescription.
I'd err on the side of caution and talk with my doctor about a new prescription. Most doctors will tell you to take all your medications as prescribed and not "save" it for a time when you might need it again. Medicines can become ineffective over a long period of time, and some can become deadly.