The task is defined by the InstructorTask object.  It contains the task_type, the task_id, and the input values.  If that InstructorTask object arrives at this point in the code, and we find that it already contains subtasks, then we know we don't need to define subtasks for it.  (I check the output because I need it to exist before returning successfully.)  And there's really no other place where the subtasks would come from, and even if they did (because something was horribly wrong), it wouldn't make sense to write over them anyway.