Diapers do not expire and are safe and okay to use for many years as long as they have been stored properly.
Although after awhile if the diapers are not sealed in the package the plastic can turn a yellowish color and they may become brittle.
But it usually takes longer than 10 years for that to happen.
However as long as you use the diapers within 10 years or so the diapers should be just fine.
It's best to keep diapers sealed in their package until you're ready to use them but it's okay to remove the diapers and place the diapers in a dresser drawer, changing table drawers etc.
Most people will use diapers well within the 10 years time frame anyway so it's usually not a problem.
After 20 years or so the diapers would probably be brittle.
Diapers are made of plastic and also SAP for the absorbent material.
The plastic is what can degrade especially if let out in the heat too long or in the sun too long.
Properly stored out of the heat and sun though the diapers should be just fine for many years.