I was the new car pre delivery guy at my uncles Dodge dealership. Never saw a full “undercoat” from factory. We sent the car out to the local guy for that. Sound deadener-rock protection came on every car. Later on some telephone company trucks came in with the grease coating covering everything underneath, a mess if you had to fix something. When dad went to work at Fisher Body in Flint Mi the man he stayed with for awhile did the undercoating for the factory, a big operation, always after cars where done. This was in 53
I have a 70 Duster this local guy did, 1” thick in places. Everything was covered. Of course it saved the underside-wheelwells from rust