Next they've got to produce the line art. (As someone who used to do this step quite often in my ID career--on far less complicated objects--I can tell you this tracing step is nowhere near as fun nor straightforward as you might think it is.)
After the exterior line art, they painstakingly do the line drawings for all of the interior parts. This would be the part of the project where I'd wonder why I didn't try to become a doctor or lawyer instead. I can guarantee you their Layers window looked like the waiting list to get into Harvard.
Finally, the finished product. There's still plenty of judgment required at this step, as they have to decide how much to reveal and how much to obscure; if they got this part wrong, it would be too confusing and incomprehensible for a layperson to make sense of.