You probably have a scratch-and-sniff book around the house … and even if the book is really old, it still works! The reason the stickers last so long is because of the “micro-encapsulation technology” used to create them.
The basic idea behind scratch-and-sniff is to take the aroma-generating chemical and capture it in gelatin or plastic spheres that are really, really small. When you scratch the sticker, you rupture some of these spheres and release the smell. Think of it like this: the smell is held in millions of tiny bottles, and you break a few of the bottles every time you scratch the sticker. The tiny bottles preserve the fragrance for years. Pretty cool!