If you go to an actual LV boutique, each piece has a notecard-sized paper with a scan code and price sticker. It is usually tucked into a pocket with the two other ID tags. The SA takes this tag to scan the item and files it away. Every LV boutique I have been to has done this; department store "boutiques" do not have these notecards.
I was fortunate enough to remember the price of my Babylone and Multicolore agenda before LV hiked it up. When I went to the boutique to purchase those items, I noticed a the "layering" of price stickers on that notecard with the new, more expensive price on top. I spoke to my SA and she gave me the former prices for both items. Score!