As @aerozol also mention, these releases are likely the ones that will be the hardest to find information about later (or even at all, right now!), which (to me) makes it all the more important that they get documented properly. If someone wants to do research into music from Australia released on cassette, the data you have added to MusicBrainz may prove invaluable.
See also previous discussion somewhat related to this here:
I really, really hope you’ll continue to add the releases you have to MusicBrainz—at your own pace. “Slow and steady wins the race.” 