John Young AMSA (Emergency response division) briefing was very interesting.
Acting on information from NTSB He explained that:
"Regular messages from the aircraft, at approximately hourly intervals during its flight. Those transmission were detected by a communications satellite over the indian ocean and with the time of those communications and the distance, Then clarified "They can't plot exact distance but sequentially they can be build up into a route the aircraft took."
The wording here is crucial, it implies that
all pings were received and from that, a 'join the dots' plot can be derived. This would be the first confirmation that all pings were received, not just the last one!
Unless the Australians are assuming this is what NTSB has done, this would indicate the aircraft has been plotted heading due south
or of course due North as the arcs are mirrored!