They'll know it when they see it, mine was 25 yrs old when I retired it after 4 repairs. Only had to pay shipping to them. I never had any proof of purchase.

Yes, this exactly. I have an 18" leather and cordura fanny pack with front zipped pocket that I used as a shoulder bag for about 12 kilos of tools. Jansport repaired it 4 times over 25 years for broken zippers and general tears on the shoulder strap and pack. I sent it in, told them how I was using it, and every time got it back with a nice note. Finally my shoulders needed a break, so it's retired. Favoritest pack after my 1972 Frostline frame alpine pack. That full size backpack is still the Bomb!