> They are struggling with what they're drawing looking wrong to them, until they're fairly far along and the shapes are fairly complete.

In general I agree, but I have a counter example. I have a friend that has always been very good at drawing, and when he draws, it's immediately obvious that he has a very precise idea of what is going to happen. People often gather around him because it is entertaining to look at the drawing and suddenly understand what it represents. It's a similar experience to uncovering a photo frame covered with dust.

I assume that this ability is not uncommon among professional drawers.