I have never, ever, ever had a perfume spoil on me.
Once, I recieved a perfume gift that was spoiled. But, I've never had one spoil that I had purchased myself.
I have even had some bottles for over 10 years, and they smell totally fresh. Sprays last an insanely long time- like perhaps the remainder of your life. Some even improve with age, like wine. Screachy notes can mellow out, and fixatives can become stronger in scent. Pour bottles can last a really long time too. I have a friend who has a pour bottle (flacon) of Windsong pure perfume, that is over 20 years old, and it smells good.
If a perfume goes rancid, it's usually because it was mistreated. It was left in a sunny window for a couple years, in a damp bathroom it's whole life, or contaminated. I keep mine in my bedroom on a dresser, way from direct sun rays from the window- they never spoil.
Hope this helps. I wouldn't even worry about it. If you don't mistreat them, they will last so long it's mind boggeling. The 5 year rule isn't a rule, it's supposed to be a promise to you made by the company...it will last at LEAST 5 years...mistreated.