Airservices Australia continues to publish the Multicom concept in its AIP Book.
and
had conflicting information from the airspace regulator and the airspace service provider
A minor point, but not well known it seems: Airservices as the AIS provider only
publishes AIP Book.
The content with respect to most of it in particular this sort of thing is firmly owned by CASA. They file the text amendment requests with Airservices who make the changes. I gather CASA did so last year and presumably did so a month or so ago for the 21 August amendments.