This split-connectors model is actually quite uncommon. Many newer cars have either a single CAN bus, a "Gateway" module which bridges Diagnostic CAN accessible

This split-connectors model is actually quite uncommon. Many newer cars have either a single CAN bus, a "Gateway" module which bridges Diagnostic CAN accessible through the OBD port to the various CAN buses used inside of the car, or Ethernet / DoIP exposed over "unused" pins on the OBD connector. For example, on modern VW AG cars, key programming is performed over the OBD connector, using specific UDS readLocalIdentifier and writeLocalIdentifier requests, but the data involved in the Immobilizer is both signed and encrypted using secret keys on a VW server (called FAZIT) over a subscription system called GeKo. The dealer diagnostic tool essentially sets up a tunnel over UDS between the Immobilizer software module in a control unit and the FAZIT server.