Never really looked at this and would have thought the quarter panel is made of one piece, obviously not. So these welding must have been made during the production of the quarter panel itself. Once it gets put on the bodyshell the exterior side is already finished off...
Nice to have some real craftsmanship on those cars. Also the quarter panel to rear center panel under the tail lights with the small crevice, the two panels are spot welded and then finished off by by an assembly worker doing brass soldering and hand finishing.
With craftsmanship also you have a bit of fluctuations in the appearance I.e hangover Monday, fight with the wife, no salary increase or so.
To identify a replacement of the panel, always look also from the inside of the trunk at the described joint under the tail light, spot welds of the quarter panel along the bumper line seam, underbody seal condition on the "fins" along the joint of the quarter panel, floor panel at the area of the side pockets of the trunk (outside/underneath)