I was having a service on my 15-year-old 2005 4runner and was watching the mechanic take off the old "serpentine" belt, so I handed him a brand new serpentine belt, and he handed it back and said the old one is fine.
The mechanic works at a shop with 6 car lifts/racks and 10 other mechanics - all working 5 and 6 days a week - with plenty of business on all brands and makes.
That was 2 years ago. All is still fine!
BTW That serpentine belt goes to the OEM water pump. Who builds a WP that lasts 15 years?