That's simply for standardisation, at least in the U.K. I have seen the stalk with the three dots on most if not all the vehicles here, whether they have ADAC or not.
My intensions with this statement was that at least the button is present as it would be useless to try ADAC without it (some cars does not have the 3 dotted stalk button). The car might still have ADAC option inside IF for instance the cluster have been previously replaced OR that the car for some reason has ADAC hardware/software present but not activated from factory. The technician replacing a cluster would in most cases print out the current configuration and use the same setup when replacing a new one (as he would when replacing a BII).
On pre CAN the instrument cluster holds all the instrument config while on CAN models BII handles all config exept hazard on/off by PLIP activation.
I will dive into the 97,98,99,00,07/00 and the 07/01 wiring book to see if there is different wiring as a result of ADAC or not but i suspect that they would not bother to issue different harness pieces on this only.