Make sure to keep records yourself. Date purchased, from where, ticket dates, ticket numbers, transaction numbers, payment method, etc. I try to keep any emails and receipts associated.
After the ticket date passes, usually a credit can still be issued on totally unused tickets BUT you cannot rely on Disney’s system to provide that info for you. The tickets may no longer show in your account, but you can help them trace it by providing details.
We’ve had to do this a few times. Normally ticket credits can only be used toward new tickets, on a one to one basis.
Example - you can’t apply the amount you paid for an unused After Hours ticket to pay for the Dining Plan, LLs or Meet the Rhinos, etc. You can’t use 3 unused After Hours tickets to pay for one multi-day park ticket, or vice versa. One ticket toward the purchase of one new ticket only.
If the new ticket is priced lower than your expired unused ticket, they will not refund the difference. So one $200
MVMCP could be used to buy a $150
MNSSHP the next year, but you will not have any credit leftover after that transaction. If you ended up not using that MNSSHP ticket and wanted to use toward one 2 Day park ticket, they will apply $150 a credit (not the $200 of original purchase).