I did a quick search and find that Mace does have a limited "Shelf Life" and since this mace in your glove box is 22 years old I bet it is inert. Oooooo, good one. Excellent.
So, he needs to have the contents tested.
Or maybe, see if the cops get it tested first, and then move to dismiss if they don't.
I wonder what he would need to do in order to preserve the contents for an independent test?
Well, from what I've read so far it most likely has a shelf life of three to five years. I'd bet that the container sit-rep's wife has is totally inert and useless. It may not even have a propellant active anymore.