Agree that any ticket cannot have a validity of more than 1 year. What I was suggesting is that the original ticket could be used as partial payment towards a new ticket. It's as if the airline gave the passenger a cash payment of the refund amount, and then took it back as payment towards the new ticket. That new ticket would have a validity of not more than 1 year after the date of its issue.
Btw, I understand that a certain national airline based in a country to the west of Japan has issued tickets with a two year validity (catering to the needs of a specific market). How they did this is unknown, but ...