The newspaper announcing the start of the war has a picture of a British tank on the front. These were not developed until a year after the war started and did not see action until a year after that in 1916.
About 20 minutes into the film when the soldiers are in the trenches, we see a box of Elmhurst tea. The Elmhurst Tea Group was not established until 1928, so it wouldn't have bee in use during the Great War.
When Billy is coming out of water after swimming in Sydney, a speed boat takes of in the distance at speeds way beyond the era.
Approximately 55 minutes into the film, when Mrs Kelly is questioning a Major about her son's status as MIA, the Crown on the Majors right shoulder is upside down.
The length of hair on the soldiers would not have been tolerated during the war. Hair was always cut short. Nor would soldiers have been allowed to grow beards.
The soldiers are infantry but they are wearing Light Horse bandoliers.
The signaller in the command post is sending the same two words - HELPI and HELPIRE - over and over.