They don't have an unlimeted shelf life, theu actually do degrade after a while, the stuff in them to absorb liquid degrades as well as the paper they are made of.
We had some left overs from our first child that we had to throw out before we could use for our second.

I never got the need to sotre items for barter anyway, why not use the space to store more of what you will need rather than what you think someone else might.