I bought a new Casablanca fan 2 years ago. It came with a lifetime warranty, provided you had the original receipt. So, I carefully slipped the receipt into a binder of important house documents. I wrote on it, too. Just so it was clear was the receipt was.
I was flipping through my house book last week and came upon a blank piece of paper ... or what seemed like a blank sheet. Until I realized it was MY RECEIPT. Ugh. If my fan ever breaks, all I can hand them is a blank sheet of paper???
If you Google "fading receipts," you get a lot of hits on this topic. Business sites and complaint sites both cover the topic. The best preventive measure is to photocopy important receipts. It seems both insane and wasteful to do this, but it seems sadly necessary.