The GTD diffuser is the same as the standard Golf's, the GTI is different. Those cut-outs seen are to suit a GTI.
Pretty sure you need standard mudflaps on the back of a GTD, and GTI mudflaps on the front to get the proper fit.
Others have already said the same. Amazed that the dealership technicians didn't figure out that those rears fitted are just plain wrong. Some techs seem to have no common sense about them at all - doing exactly what the instructions from VW say (to the letter) and don't have enough practical engineering know-how to realise that what they've done is wrong and therefore their instructions are wrong.