Science demands that if new data does not support your theory, then it’s time to change the theory! So it is with history. Despite the fact that the Australian Archaeological Association quoted the Australian Glass Manufacturers trademark as dating from 1934-1948, it is not correct.
The Australian Glass Manufacturers Company Limited date from 1915 until 1939 when the company became Australian Consolidated Industries Ltd. I think the trademark above was modified slightly, but indeed did change.
In Trove there are entries in the Commonwealth gazette of A.C.I. producing plastic buttons for the Department of Defense, but not A.G.M. I have two sizes of black plastic RAAF buttons and one brown AMF button with the ACI trademark on the back.
I have not found out when the A.G.M trademark was first used, but perhaps a glass bottle collector may know?