Extraordinary claims require extraordinary proof and at least here in this so-called "third world" country plenty of people makes their clothing to be repaired in any way or do it themselves (even me, sometimes)
I had at least z dozen zippers replaced through my life. Some times you a very good product with poorly chosen zipper, some times it is some sort of an accident.
I find the idea of buying a new coat instead of fixing a small part of the old one weird.
I'm afraid YKK might not be generous
I guess it's just cost of repair vs cost of garment. I always opt to spend $15 replacing the zipper than to buy another coat or whatnot.
You'd need a way to hold the zipper teeth and the fabric in place while you stitch. Maybe temporary tape or some special-purpose jig thing.
You just get an extra semi rigid fabric track when you repair. Your clothes should still work.