Percocet used for pain relief is a narcotic medication and prescriptions can prevent people from getting high on Percocet without medical reason.In fact, the Percocet high feeling can get you into lots of problems.
I think the formula of the perfume itself decides how fast it will spoil. My perfumes from Britney Spears Curious and Salvatore Ferragamo went bad within a year and a half. The Britney Spears one developed some precipitation and started smelling like alcohol, while the Salvatore Ferragamo just smelled plain weird.
If you want to compare a fake perfume with a real perfume, you shouldn't compare them when first spraying, but see how they both smell on your skin after 2 hours, 4 hours and 6 hours. A cheaper perfume may smell bad or have no smell at all.