There's different assembly is probably because the lights are little differ for Europ spec, and US spec. US spec has little red light that lights up with parking/headlight when the lights are turned on.....and Europ spec will have a orange reflector in place of the lights....
P.S. For anyone who doesn't know what I am talking about. Go find a pic of both US and Europe spec. Compare the taillights. US spec will have a red cover with lights in it. And right beside rear turn signals(W126).