I, too, had a stack of old tickets and wanted to double check to be sure none had days left before I pitched them. So on my last trip In November, I had the Cm at Guest Services in MK scan each of them and was surprised to be told that one of my old tickets had one day's park admission remaining. BUT when we tried to use it the next night (at the MK, interestingly enough!) it was rejected at the turnstiles and we were told to take it to the ticket booth near the gift shop (to the right of the entrance before you get in). The CM informed us that, yes, there was in fact a day that had not been used but that it had expired. I have no recollection of EVER buying expiring tickets (never bought length of stay or anything like that)...anyway, the good news was that the CM offered to re-issue us a ticket valid for one day (all we wanted was that few hours in the MK to see the parade so I guess it was no big deal to Disney but it was, I thought, a very decent (and Disney-ish!) thing for them to do.
The point...checking old tickets is not always perfect!!!
(By the way, now I write on my tickets the # of days remaining at the end of a trip to help with planning the next one)