I purchased my bag preloved and had it exchanged at the store on Tuesday for the crease. I have made it a point to purchase preloved bags with a reciept only since I've heard they ask for them. They did take a picture of the receipt when they were accessing the bag and they kept it when I made the exchange.
I usually make it a point to buy preloved with a receipt too- and was going to go against my belief and purchase an expensive preloved item (speedy b empriente that's known to have issues with glazing at times) without one because it was discontinued but after reading this i take it as a sign. I would hate to spend 3k on a preloved item that LV wouldn't repair or spa without a receipt if a prob occurred.