Yeah, supply/demand can fluctuate the cut off each year. Some courses have been known to fluctuate +/- 3. Also some years, if there is a big change in how unis decide to run the course(i.e when UTS decided to offer more places in their journalism degrees)-it was 97 in my sister's day, it's now 89.
Some course have fixed ATAR entries though (like Adv Science is always a flat 95 at most instituions).
If you are in some kind of scheme i.e early entry, a guarantee cut off (like E10, KLD, SEAS melb cut offs, other equity cut offs)-early entry you are already in the course, and the others are all a form of provisional entry that you will absolutely get in if you meet whatever X score they specify (though sometimes the criteria can include a Band X in a subject area).