Genuine W111 coupe and cabriolet bumpers are described as hideously expensive and virtually impossible to source, so many cars wear W108/W109 sedan bumpers as a cheaper substitute. Sharp-eyed commenters routinely flag these swaps, which knock the presentation and correctness of otherwise nice cars.
Original coupe bumpers are effectively unobtainable
Mercedes-Benz W111 Coupe / Cabriolet · cosmetic