With Success one textbooks (I used it for Chemistry and it may have been the reason why I and another BoS'er I know missed out on B6), they tend to have answers that go a little bit in excess and have way too much information that barely any students could all right in the final exam or on time.
Though the structure of the success one answers are a little off to what the HSC markers want you to structure your answers.
I used some other past paper book for Physics (with the blue cover and moon) and it was a little better but the information in that was sometimes out of scope too. I got B6 but then again that could have been due to personal reasons rather than a textbook.
I would recommend that alongside these textbooks, you use the HSC marking guidelines and sample answers as I would say if it weren't for those, my answer structure would have been a little off and I would have lost quite a few marks for both Physics and Chemistry. I would say the same for the past paper textbooks because some of them have really useful info on how to "fine-tune" your answers.
To answer your questions:
- They are answers that the author would expect to get full marks (they are NOT board endorsed). However most of those answers would get in the top band any way.
- Use marking guidelines, use the sample answers provided by BOSTES and use the past paper textbooks. Note that the sample answers by the Board are said to not score you full marks but are a general guide (though realistically 90% of those sample answers would get full marks in the exam from my experience).