somebody must have fitted the rear discs to the gti as they never came with them, theres 2 options on rear discs either its the rs2000 rear beam thats been fitted or the st170 version, you can normally tell by a quick look at the discs themselves as 170 ones are shallow where as the rs ones are deeper as they have shoes inside the disc for the handbrake and pads outside for the actual braking which is a stupid design tbh and you will need the handbrake cable for sure