If I am remembering correctly, a few years back they made a major change to the "forever" pass. From what I understand they still honor it but only partially. In order to get to use it you have to go to one of the ticket kiosks and they will figure out what that ticket cost when it was purchase and credit it toward whatever the current price is when you use it. So if the original ticket cost $30.00 and the current price is $100.00 you have to pay $70.00 more to get in the park. I don't think it carries the park hopper perk either. That would be extra. Someone correct me if I'm wrong.
I think when they first ended the never expiring ticket they did accept them as full payment for entry, but shortly after they decided that just giving a discount would mean that what was paid before could count as a credit to the full price.
Absolutely everything I've
ever read, heard, & seen (including Disney!) says Disney has always/only honored the
full day(s) remaining. The tickets are just like "Forever" stamps; no matter how much first class postage skyrockets, the price I paid for that stamp guarantees the 1st class delivery whenever I decide to use it (don't want to open a "Pandora's box" on the future of USPS lol). Disney proudly promoted
back then that tickets "never expired."
Besides, I doubt there are all that many "unused" tickets floating out there (nevermind how many likely get thrown away b/c they're either mixed-in with other papers or whoever finds them doesn't think they're worth anything, etc, etc, etc), and no-doubt Disney took all that into consideration (for example, everything they sell now certainly has an "expiration.")
IF Disney ever were to try any inflation-adjustment-penny-pinching BS with me, not only would I never give them another penny again under any circumstance, but I would use my story at every opportunity to encourage everyone I knew to do the same (nevermind the plethora of other examples given through these forums and elsewhere).
However, I don't know of any instance of "Park Hopper" being included when someone redeemed an old ticket, which I'm fine with. I consider "Park Hopping" too much work now lol.
Besides (one more time) Disney still wins here with all the money spent for food, souvenirs, etc.