Cactuar's can also break the 9999 limit. Compare that as well. Those are the only two that can.I'd also imagine that there's the possibility of exact damage in Cactuar's. It's probably going to be stored as a two-byte exact value rather than a multiple like FF7's (Omega Weapon's Light Pillar always does 9998 dmg).
Quistis' Final limit break can do more than 9999 as well.
Huh. I didn't know that. I guess she's always been weak when I used it or I wasn't paying much attention.