GCM: MulticastResult - which result is from which device?

Following the last section in the GCM: Getting Started guide, there's some book-keeping to be done after receiving the results.

Quoting from the guide:

It's now necessary to parse the result and take the proper action in the following cases:

• If the message was created but the result returned a canonical registration ID, it's necessary to replace the current registration
  ID with the canonical one.
• If the returned error is NotRegistered, it's necessary to remove that registration ID, because the application was uninstalled from the device.

Here's a code snippet that handles these 2 conditions:

if (result.getMessageId() != null) {
 String canonicalRegId = result.getCanonicalRegistrationId();
 if (canonicalRegId != null) {
   // same device has more than on registration ID: update database
 }
} else {
 String error = result.getErrorCodeName();
 if (error.equals(Constants.ERROR_NOT_REGISTERED)) {
   // application has been removed from device - unregister database
 }
}

The guide above refers to a single result, and not to the multicast case. I'm not sure how to handle the multicast case:

    ArrayList<String> devices = new ArrayList<String>();

    for (String d : relevantDevices) {
        devices.add(d);
    }

    Sender sender = new Sender(myApiKey);
    Message message = new Message.Builder().addData("hello", "world").build();
    try {
        MulticastResult result = sender.send(message, devices, 5);

        for (Result r : result.getResults()) {
            if (r.getMessageId() != null) {
                String canonicalRegId = r.getCanonicalRegistrationId();
                if (canonicalRegId != null) {
                    // same device has more than on registration ID: update database
                    // BUT WHICH DEVICE IS IT?
                }
            } else {
                String error = r.getErrorCodeName();
                if (error.equals(Constants.ERROR_NOT_REGISTERED)) {
                    // application has been removed from device - unregister database
                    // BUT WHICH DEVICE IS IT?
                }
            }
        }
    } catch (IOException ex) {
        Log.err(TAG, "sending message failed", ex);
    }

I submit a list of devices, and receive back a list of results. The Result object doesn't contain the registration id, but only a canonical id if the first is obsolete. It is undocumented if the two lists are co-related (ie. preserves order and size).

How can I be sure which result refer to which device?

-- UPDATE

I've pasted a snippet of the solution in a separate answer below