I have checked tickets at WDW, the CM who helped us was fairly new so it took way too long, but I think generally it should be a quick answer.
I did find this on another site??? but haven’t tried it myself yet but will soon.
[I][B]Checking Days Left on Used Ticket[/B]
If you have left over park tickets from previous visits and can’t remember how many days you have left on them, you can have your ticket checked while at Disney World or you can call Disney to check their status:
407-566-4985 - Option #2
NOTE: This service is only available Monday - Friday from 8:30am - 4:30pm.[/I]