I know for other subjects there might be some areas of similarity with the year 11 course, but is math the only subject that specifically assesses year 11 content?
my school only offers a limited range of subjects so idk about a lot of them, but out of eng, maths, sciences and other subjects (the more popular subjects in selective schools, sorry idk how else to say it), yeah maths is the only one that assesses y11 content explicitly.
but from what i have seen, if you have a y12 topic that is very similar to a y11 one that you did, there are chances they will expect you to know your y11 content. a lot of my subjects deliberately model all of our y11 content to match with y12 e.g. for modern, my teacher knows we will do the cultural revolution to tiananmen square topic so she made us do boxer rebellion and chinese revolution stuff this year. chances are she might assess some of the stuff we did this year in y12. obv she wont ask us a straight up y11 question but she will adapt some of that y11 content and expect us to be able to use it when interpreting y12 questions.
in that sense there are some chances your y11 content will show up on your hsc internal tasks at least. you probably don't need to revise y11 content for hsc directly for subjects other than maths but if you are covering a similar y12 topic, revising a bit of the y11 content to build on your depth of knowledge can't hurt