If you check out VW Heritage they offer two types of discs, The difference I think is the
'depth' of the flange from the hub bolts to the disc braking service.
Of course you may have early spindles and early discs. Early calipers use smaller mount
bolts/holes and have thinner pads although I must say to a casual glance they do look very similar
Searching the topic here or VZi should yield more details.
Cheers
James