To the OP, here's a picture of an original, well-preserved, never been re-welded or re-painted late model rear quarter and door. Note the lack of weld at the rear sill joint, and good alignment of the curved door corner. If there was some other market that received this "reinforcement" that...
I highly doubt these are factory. All the above photos show evidence of body work that deviates from factory construction. Alignment is poor. The 4 wheel drive emblem is riveted. All the paint is too deep and shiny to be original. The curve in the lower door panel which started in 1/79 is...