This is what you would find after cutting a windscreen away from the adhesive which keeps in in the car.
Note, there is an extra blob inside the 90-degree turn. There’s another one on the opposite side:
This windscreen had been replaced. To be fair, it wasn’t a bad job; just a little messy in places (the interior A-pillar covers hadn’t been removed, and the previous installer’s bond line was on the fabric which meant they couldn’t be removed before cutting out the windscreen). These extra blobs of polyurethane were of particular interest.
Underneath each blob is a hole. A hole to accept a locator on the windscreen (like a dowel) which helps set the windscreen in the correct position. The locator (usually on genuine parts only) drops into the hole and leaves a tiny bit of wiggle room, all within tolerance. It is especially useful on the assembly line as it negates the need for someone to check and measure the glass position before taping the windscreen in the correct position. It’s also useful for fitters as the locators are precise in their placement which means you can’t get the windscreen in the wrong position. Some fitters, however, don’t like them, and they would rather remove them before fitting the windscreen. Their thinking is that it could cause a stress fracture (which would only happen if the windscreen was bedded down evenly).
Aftermarket windscreens normally do not come with locators or setting blocks (very rare if they do). This means the holes on the car for those locators are redundant. They’re not needed.
The case in point here is that the hole, whether you use it or not, is inside the bond line. Take a moment to process this. The bond line is what adheres and seals the windscreen to the car. It’s watertight. No air, nor water, can get past or through it. It protects the inside of the car from the outside (as well as adding a degree of structural rigidity to the chassis). So why has our friend blobbed the holes in? They’re inside the bond line.
Plugging the holes with polyurethane would make sense if they were exposed to a water risk, but they’re not. If the windscreen did leak, it would leak because the bond line was breached or that the preparation was not adequate. Not because the holes weren’t plugged? In any case, when the genuine windscreen was in place, there was a location dowel in the hole. Or did this fitter thing they were plugs to keep water out?
Return of the Hole
Not all donuts have a hole and not all holes have donuts around them, so every mistake is relative and every perfection is subjective. Some people are just good at being shit, eh?