What they were "supposed to do" and what they did varied.
All the blackout was painted after body color...otherwise there would be no reason to note on the drawing that the black was not to be painted on certain color cars.

The cowl was painted across the top(of course) and some amount of paint went under the back corners of the fenders on the cowl.(I've seen it puddled there) The edge where the black cowl meets the firewall was NOT a sharp line (tapped off). It was fogged, indicating it was sprayed at an angle from about where the windshield would be. In some cases the black shows up on the firewall in spots.

Many people miss the blacking of the frame in the front wheel well as shown in the drawing.
Everything that would be seen through the grill should be black.
Then the pinch welt.
I have also soon factory black paint in the inset of the taillight panel where the frame of the taillight surround attaches to the body. The taillight surround outer edge is, of course, black on a Challenger. so painting black in the recess would keep that bit of lighter body color from being seeing.

My guess is the guys on the line did whatever they did as quick as possible and often ignored/missed certain areas as well.
As noted, by the middle of the 70 model year many of these details went away with more following each year as cost savings, no-doubt.