E28 5er - Interesting unknown rear wing/spoiler... Hartge maybe?

A lovely barn-find shot of an E28 528e in the USA, but on closer inspection it sports a striking rear-wing/spoiler that I have never seen before. Who makes this piece? On first impression I would say one of the period Euro-tuner firms like Zender or Hartge, but after a bit of research I can't find an identical one. The chrome-trim makes it look as if the spoiler was fitted later on though and the car is not a tuner model. Perhaps someone can shed light on this spoiler's origin?

Hartge lay claim to a few E28 aero-parts and a I can find a couple of similar rear-wings, pictured below. The upper one is a rounded type and I am not sure is definitely made by Hartge though the badge suggests it is, and the second pic shows a Hartge developed E28 with their own rear-wing fitted, very similar to the one at the top but not quite as tall and curved on the top-edge not flat. It could well be that it is a similar version of this same spoiler and still made by Hartge, but I cannot find it.