Diapers including parents choice diapers don't really expire although overtime they might turn a yellowish color but it doesn't affect the performance or absorbency of the diapers.
However I've noticed that some diaper packages state an expiration date but really you can still use the diapers past their expiration date without any problems.
If you think about it disposable diapers actually take a very long time to decompose in landfills which is at least 500 years so it would take a really long time before the diapers got to a point in expiration where they couldn't be used.
If the diapers are stored properly and kept out of damp areas and sunlight then the diapers should be just fine.
I've used diapers on my kids past the expiration dates without any problems.