I'm not sure about the disc, but check this one out,
my mk3 gti, needed new brake pads in the front, so I rang local motor factor up, he said bring old pads down so we can match them up,
Nway took then down, and the pads he matched them up with, were mk4 pads, but the mk4 have abs clip sort of thing, so for me to use then I had to chop em off, but the point is, I have mk4 pads, he matched them up using the brake world book, and literally put my pads on the page of the book to match the size lol
ever seen this happen before?