I think Collector's Mode should save optional drawings too...

[MikeyVah]

Say, you missed a drawing in one scene and you want to do it after finishing the episode, you could just go into that scene in Collector's Mode and do it. The game doesn't do that at the moment of posting this.
Maybe this could be added in a future update?

[Riddler]

No, because the drawings are no collectibles, they are part of the story and if you do them, they appear in your sketchbook. And the sketchbook is your story-diary.

[Sparkless20]

Originally posted by MoikeyVah:

Say, you missed a drawing in one scene and you want to do it after finishing the episode, you could just go into that scene in Collector's Mode and do it. The game doesn't do that at the moment of posting this.
Maybe this could be added in a future update?

The drawings are more like diary entries. Max Diary in season 1 for example changed based on your choices and so does Seans sketchbook.