A roof in central Oklahoma does not fail the way a roof fails in a mild climate. It gets bruised by hail in the spring, lifted by straight-line wind through the summer, and baked between storms. By the time the shingles look tired from the ground, the underlayment and flashing underneath are usually the parts that have actually given up.
That is why we replace roofs as a system. New underlayment, new drip edge, new flashing at every wall and penetration, and ventilation corrected if the attic was never breathing properly in the first place. Shingles are the part you see. The rest is the part that decides how long the roof lasts.