They don't, but now you need to ask yourself if the assessments that you sat were of HSC standards ??
What good is achieving 90% or 70% if those school assessments are way too easy compared to the HSC exam? Similarly, what good is coming first if those school assessments are way too easy compared to the HSC exam?
Questions like yours are usually misguided because you might not have achieved that desired 90%+ in your assessment but you're highly ranked, so some sort of clarification or validation is needed.
You should recognise that if your school historically does poorly in the HSC (i.e. not many Band 6s), then it's likely that your school assessments aren't really as hard as the HSC.
If you are not able to finish your test, but still come first, all that says is that your entire cohort didn't do well and you're at the top of group of students at the bottom. In this case, you shouldn't even be asking about your mark or your rank, you should be more concerned about your own understanding of the content and exam technique. If you can't recognise this now or you don't accept this as a possibility, then unfortunately, you may be in for a rude shock when you sit the HSC exams.