Never saw pinchweld blackout on the original '68-'70 B bodies I've owned - 4 blue, 3 green, 2 red, 2 white off the top of my head - but I never owned an original high-impact '70 B.
Most all were St, Louis, with an L.A. and few Hamtramck cars in there, Road Runners & Chargers, one Satellite.