Crado was merely a Fallen Jedi and never a Sith Apprentice or a Sith Lord. According to the Rule of Two, a Sith Master can only take one Sith Apprentice and the Sith Apprentice becomes a Sith Lord. Exar Kun’s Sith Apprentice, however, was the Fallen Jedi Ulic Qel-Droma. Apparently, Kun never had much respect for Crado, despite or perhaps due to the Cathar’s idolization of the Sith Lord.