Up to KotOR II, that is. That said, with the Revan novel's retcon on how the Sith Triumvirate killed tens of thousands of Jedi, and the fact that the Triumvirate's assassins seem to be hierarchically organized in accordance to the number of kills they've made, I wouldn't be surprised if the top assassins (including Sion) killed dozens of Jedi. Nadd's blaster would've killed more.