Blacked out before any additional panels are added to the car. Near about the same point in the assembly line when the engine compartment, radiator support and such were painted black but a different station and process. This produced a little or allot of paint (with overspray extending inward) spray onto the floor and panels (such as front frame inward from the pinch weld) that hung down. If little the paint application was thicker since there was less area covered so the amount was greater with it did get sprayed.
This also produced a thin ribbon of no or misting of paint where the pinch weld created a shadow on the inner side of the pinch weld as well as immediately next to the rocker.
During the application of the pinch weld black out the gun/spray once it got to the front edge of the opening for the rear wheel well, would typically spray black onto the leading edge/area of the inner wheel well where the sound deadener and exterior paint had been applied at prior stations. The same thing happened at the rear of that some inner wheel well where the spray application of black started again to the rear edge of the quarter panel. This typically produced (in addition to it over the sound deadener and exterior color in the wheel well, black being applied over the rear frame rail directly below the wheel well panel and extending back on the frame rail 8-12" rearward. Often far enough back to be seen around the forward, outer edge of the bare (treated) circle left by the dolly the body was attached to at the time
Hope this helps explain the details well enough