Wii disc games have ticket too.
that's what allowed the user to copy the savegame to the console. without inserting the disc (just inserting, even without launching it) you couldn't copy a savegame for that game.
or maybe I'm mistaking with another file where all played games are stored. but disc have tickets, it's used to decrypt the disc!.
If the tickets are bad when extracting the wud with current extractors, then it means the tickets are not installed as "eshop" games, but as disc games using the proper (fixed) ticket that the disc contains.
editing the ticket is actually fixing it, not modifying it to make the console accept it as an eshop game.
if you already played that game disc, the ticket is already on your console. but to install the game into the console you still need that ticket to validate the decryption of the encrypted files from nus.