Hey, @PatrickHallberg, I bought Diamantina Cocktail as a kid and haven't listened to it in years. Your question really brought back some memories for me!
So here's the story: There are two versions of Diamantina Cocktail — an Australian version that came out in April 1977 and an international version that came out a few months later, once "Help Is on Its Way" started climbing that charts.
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The international version — the one you and I are familiar with — is a nine-track album that combines cuts from the original Diamantina Cocktail and the group's previous Australian album, After Hours. The version on Spotify has the original Australian track listing.
This sort of thing used to be fairly common with acts as they began to find international success after they already had achieved some renown in their native countries. The most famous case is The Beatles: British and American fans grew up with markedly different catalogs - albums with the same names but different track listings, as well as compilations in one country that the other never saw. (When The Beatles catalog moved into the CD and streaming ages, everybody got only the British versions of the albums.)
As I've pieced things together, here's what happened with Little River Band: They released their first album in 1975 and achieved enough success, particularly with "It's a Long Way There," that their manager started pushing them in other countries and secured a U.S. record deal.
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But by the time "It's a Long Way There" finally made its way onto U.S. airwaves, the Little River Band was ready with its second album, After Hours. The U.S. label passed on After Hours, but when "Help Is on Its Way" took off worldwide, the label took their favorite songs from that album and the Australian version of Diamantina Cocktail and released that compilation. By the time Sleeper Catcher, came out in May 1978, the Australian and American labels were on the same page, and that album — with its massive, worldwide smash "Reminiscing" — was the same everywhere.
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If you want to listen to the album the way you remember it (and why wouldn't you?), my suggestion would be to create a playlist recreating it with the tracks from the two Australian albums. That's what some of my American friends have had to do to experience The Beatles albums from their youth.
Hope this answers your question!