There really was an Australian girl group in the 60s called The Sapphires but they only had three members not four. When they were invited to tour for the troops in Vietnam, two of the group declined due to their anti-war stance, so the remaining Sapphire drafted in her sister to help her out.
The opening scene shows a girl running through a field of canola in 1958. The first canola in Australia was planted in 1968, but was not grown commercially
until the 1990s.
Throughout the movie the girls are seen performing on Shure SM58 Microphones which were released in 1966. This is chronologically correct as the movie is set in 1968. However when they are performing to the 19th Infantry Division in Nha Trang, the microphones being used are Shure Beta 58 Mic's which weren't released until 1989.
Dave: Before we go than, girls when I met you you were doing all country and western thing and that's fine we all make mistakes. But here is what we learn from that mistake. Country and western music is about loss. Soul music is also about loss. But the difference is in country and western music, they've lost, they've given up and they are just all wining about it. In soul music they are struggling to get it back, they haven't given up.