I have seen many cars lately with gates/dayco/dmch belts installed with one of the edges frayed. This is caused by an issue with the pulley alignment. You can tell which way the pulleys are belt by the side the belt is worn on. Also if you have a VERY loose idler bearing that is cocking the pulley under tension this can also cause the belt to ride unevenly on the pulley.
Another notable thing to check for is corrosion on any of the pulley's. Cars that have sat for a period of time develop mild scaling on the pulley grooves where the plating has either been compromised or worn off over the years. This acts like sand paper on a rubber belt.
The final failure can occur from incorrect installation of the entire pulley bracket assembly. If you have the incorrect shims installed or in the wrong locations etc you will have the same issue time and again regards of how many belts you install. It will be a dead give away if it is installed incorrectly. But the bolts are long enough to put the spacers in backwards and still seal the timing cover o ring plate.
and the final comment of the day. Always be careful installing the two bolts that thread directly into the timing cover. It is very easy to destroy the threads on the two holes. It is possibly to helicoil the threads in car with the proper tools without removing the cover, yet it is anything but fun to do. If you pull either of these bolts out and see aluminum threads on the bolts immediately repair prior to installation again. If you run the bolts back in they will back off with two results. Throwing a belt and a nasty oil leak down the front of your engine.