I have seen some lower priced and generic off name brands of supposed ice and water shield materials, which were nothing other than a glorified silica sand coated base felt paper.
The adhesion qualities of most of the brands are far inferior to the Grace Ice and Water Shield. I would not be surprised in the least, if the nail holes have not been sealed by the elasticity, or lack thereof, of the product used.
The sure seal technology, does not offer a water-tight seal, but just more adhesive strength for wind blow off.
Water flowage can go backwards under the shingles by cappilary action, thus finding the nail penetration holes and will leak all over.
It sounds as if they “Added” a gable vent to the attic environment, which minorly be a concern due to the short circuiting ventilation theory. I highly doubt that to be very practicle though, since there is such a minimal attic cavity on a 2/12 pitch to begin with.
Ed