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Apropos of nothing - a random HP thought.
Where does half the fandom get the impression that Harry is cheating by using a book with notes in it?
They are allowed to use their book while brewing and are supposed to have read up on the potion they are preparing in class.
And in written tests, I doubt they are allowed to use their books anyway, so the notes won't be any help to him there.
The only difference I see between Harry and a Ravenclaw (in this instance) is that the Ravenclaw would have made the notes himself - and probably not in the book, but on a spare bit of paper.

no subject
As someone else said, the closest subject to Potions is probably cooking. As I've never taken Home Ec, I'm not sure of the grading system there--if you were baking cookies, your mother had always put in lemon instead of vanilla, you did it that way, and they turned out better than everyone else's, is that cheating? Would it be cheating if you'd brought in a recipe from _Good Housekeeping_? And what's the difference?