SAM, with my final HSC marks, predicted me at 99.7 - which is exactly what I got
so it was 100% accurate for me.
Another one of my friends was predicted at 99.8 - which turned out to be her UAI - whereas another friend was predicted at 99.6 by SAM but then got 98.9...so its accuracy can definitely vary...
During the school year, with very rough [and marks that turned out to be slightly lower than my final results] marks, SAM predicted me consistently at 99+, but more like 99.1-99.3, that sort of thing...