Get QUEUED_MESSAGES should only be sent to the root device, so only the root devices should include the PID in its list of SUPPORTED_PARAMETERS.
If the responder responds to the request with a queued message it can set the sub-device field in the response to match the relevant sub-device. To reiterate: The Request is sent to the responders root, but the response can come from any sub-device.
If the responder responds to the request with one or mote status messages, the the response sub-device is always zero (root), but each status message within the response includes the sub-device
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