We went to WDW in January and I had one partially used non-expiring 10-day park hopper. There were 4 days left on the ticket.
(it was great, back in the day, when you could get a 10-day ticket and they never expired. The tickets were good for two trips and saved us money and then the Disney Corp figured this out)
Our trip was for 5 days so I bought new 5-day tickets for the family. I only had 4 days on MY ticket so I asked if I could add a day to the ticket. They told me the ticket was too old and that they couldn't do it. I had to buy a 1-day park hopping ticket for something like $135.