I think units that randomize into journeyman, pupil, and recruit classes start off as the 2nd tier of the class. They'll act as a basic unit that will either promote into a normal promotion or the 3rd tier "Super Trainee". I think it has to do with the fact that the auto-promotion is triggered by a conversation after a mission, prior to reaching level 10. And since Ewen, Ross, and Amelia are the only trainees, the randomizer must be programmed to only randomize into 2nd tier trainees to avoid crashes or units that will stay stuck at level 10 and never be much help. That's just my guess anyway.