I'm not quite sure why you think it would 'communicate' with the rear doors locks separately?
Each door module has a unique CAN bus address. Each module contains a PCB with a microcontroller and some CAN bus interface chips. Each microcontroller has an integrated area of ROM which contains such things as version information and the CAN bus address - Each module is 'handed' so it may only fit a specific door. All electrical functionality for a particular door is handled by the exchange of messages between the central convinience module and the door control module. Any operational failure during the exchange of messages is logged in the central convenience module. The log messages may be extracted by VAG COM or the VAG service tool (just like an engine ECU log).
Car technology has moved on a bit since the introduction of electric windscreen wipers and wind-up windows : )
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