How long does prescription medicine keep its potency?

I have a prescription for Flexiril that I take very rarely. I had 3 refills on the bottle that expired a month ago, which I never filled, so I’m guessing it has been at least a year since I filled the bottle that I currently have.
I still have a ton of pills left in this bottle… I really barely touch them [I hate taking any sort of medicine], so are they still good? Should I be calling and asking for a new script?