My neighbor ended up footing most of it himself, unfortunately. He'd missed the warranty registration by literally a week or two, and the manufacturer wouldn't budge. Pretty frustrating to see happen, honestly. And yeah, you're spot-on about double-checking deadlines and paperwork. I almost missed mine too because I assumed the roofing company handled it automatically—turns out they didn't.
One thing I'd add is to snap a few quick photos of the install process if you can. Nothing fancy, just some clear shots of the materials, packaging labels, and the crew doing the work. Had a friend whose manufacturer tried to deny coverage because of "improper installation," but those quick phone pics saved him a ton of hassle. It's easy enough to do, and it's cheap insurance if things get messy down the road...