Sword stained with Royal Blood (81) cast error?

[Michael Kistner]

Cheung King Yu is listed in the hkmdb cast list. But her name is not on the poster, HKFA and the movie opening titles.
Now I ask me why she is listed. Her listed role name belongs to a character played by a actor who must be in the cast list (If Cheung King Yu is not correct it could be Cheung Luen Fai who plays the role).