All cars received wheelwell undercoating that was applied after paint.
As mentioned sound deadening on the inside of quarter panels (& doors), was applied before assembly on the car and was painted over.

Cars ordered with the J55 sound deadening package received additional undercoat on the floor pans and an underhood pad (on non fresh-air hood equipped cars).

All of the above were applied at the factory.

Dealership & aftermarket applied undercoating was usually a thinner & smoother appearing material.

Rick