TBH, if a subject isn't included in common ATAR calculator websites, chances are the candidature of the subjects are very small. This makes it really difficult to predict scaling, and it can be set to change from year to year depending on the candidature of students that specific year.
TBH I found IPT harder than software. There was just so much stuff to memorise. I did find the HSC content quite boring and basic however. It got a lot more interesting when I started reading deeper into the material and beyond the syllabus.
The Excel textbook is very concise. It's good for covering a lot of content in a short time. The flashcards at the back are also very useful. It's a good textbook, but often times I find it lacking in detail and use Davis to fill the gaps
IMO, most of prelim content isn't too important for the HSC IPT since you essentially learn them again anyway. The most important thing I would say is to have a very deep understanding of the 7 information processes. For any given information system, you should be able to describe the...
Ranks are more important (and gaps in marks between ranks). But in most situations, a single failed exam will not end a chance at a 90+ or even higher ATAR. Just work harder for your future assessments.
Don't worry about what has happened. Focus on how you can work to improve on the future. Your chances of 90 ATAR are not over yet. Just keep working even harder for your next assessments. Also make sure to actually analyse where you made mistakes so you don't make them again.
I'm pretty sure it is only USyd that is doing this kind of thing. UNSW states that you may still receive an offer despite scoring lower than the guaranteed selection rank.