Factory underside finish and rock guard

i think the factory workers had disposable template (probably cardboard) that shielded the general area around and including the upper A-arm which is bare metal.They sprayed to black out and sound deaden the wheel wells and frame area..The amount varied and could be quite sloppy.
The lower A arms were dipped in Cosmoline just shy of the ball joint mounts.Cosmoline is a waxy shellac concoction for corrosion resistance.As for the other components anything that required adjustment or had threads was left bare.Can you imagine adjusting the components if the threads were full of paint or undercoating?
There are restorers that have this stuff all documented.