I found this information:
Previously, students have been assessed on related texts in both in-school assessment tasks and in the final HSC examination.
2019 HSC students and beyond will only be assessed on their related texts through in-school assessment tasks.
This means you will not need to write about your related text in the final HSC exam. Win!
Need help finding related texts for Texts and Human Experiences? Read our list of recommended related texts for the HSC English Common Module!
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The question here is whether students can be assessed on related texts in their trial exams considering the trial exam is an internal assessment but it's also meant to give an idea of what the HSC exam may be like. The answer to that is most likely no - I sat the CSSA paper in 2019 and we weren't assessed on any related texts for the Common Module.
I hope this helps!