Long term failure rates are not usually measured in realtime but in deliberately heat elevated environments which simulate many years of stresses in a few month

Long term failure rates are not usually measured in realtime but in deliberately heat elevated environments which simulate many years of stresses in a few months. This work is essential to ensure design decisions they've made don't accidentally cause their chips to fail after 2 years (which might be outside warranty lifetime but would still result in class action law suits and horrible publicity).