In the northwest probably the most common form of upper roof ventilation I see is the ridge vent. This is basically an opening along the ridge of the roof which is covered with a vent and then shingles go over the top of that. While these are an excellent form of venting, usually used in conjunction with soffit venting as well, it is not uncommon to find the shingles damaged or torn off, usually due to high winds.
Due to the location of the damage on the roof, this deficiency probably would not have been visible from the eaves or the ground. One had to be up on the roof to see it. Sometimes, in this job, it is not possible to go up on the roof but, when that is a necessary limitation, it is always possible that a significant problem will be overlooked.