This would be fine if he only ever showed his face to other Sith, such as Darth Maul or Darth Tyrannus, but he appears to others as Darth Sidious several times. One such instance occurs in The ...

Just after killing Satine and taking Obi-Wan prisoner, Maul comes face to face with his old Master, Darth Sidious. Sidious had heard of Maulâ s exploits and decided his former pupil was ...