My sunglasses were checked at a LensCrafters location and they said that the UV is built into the lens material and not a coating. They said the same at a Pearl Vision location.
My sunglasses tested at 100% UV protection after having them for 5 years.
It is a surface layer on the lens. Depending on the amount you wear them, the care you take cleaning them and the climate you live it will become less effective over a year but certainly its much longer than a year.