The fact that not every section dealing with a specific character calls him by that certain title does not mean he isnt the Dark Lord And while the movies are the highest form of canon the next level is still canon and it doesnt interfere with the continuity of the movies Speaking of the movies Sidious is referred to as the Dark Lord in the prequels so in the highest form of canon he is the Dark Lord of the Sith and mentioning that title in every Databank entry he appears in would be unnecessary