I had laid off riding for about a decade due to financials. When I got back into a bike I made a trip to one of the local dealers to look for a new lid. It just so happened that their Fulmer factory rep was there that day.
So I'm checking out some helmets and the rep. is making small talk. He asks what I'm wearing now. I tell him it's an old Shoei that I've had for a dozen years, ten of them in basement storage.
"Oh no! You really have to replace them when their five years old, whether they've been worn or not. The materials start to break down." he blankly stated.
The helmet I was looking at was a Fulmer and they put a "born on" date inside their helmets. The "brand new" one in my hand had a born on date that was almost two years ago.
"A five year lifespan, eh?" I ask and he nods in agreement. Then I show him the "born on" date inside his own product and ask "So since this one has 40% of it's useful life gone, is it now 40% off?"
He mumbled something and slunk away.
I think there probably is some science to it, but I also think they should pro-rate the price accordingly, just like day-old bread and milk that is close to expiration date.