Specific passages will nevertheless generally fall under specific branches/themes, which means you can very well prepare for virtually ever single passage within the text by simply working out a response for every branch/theme. Indeed, I would argue that writing out an interpretation for every major branch/theme is essential to succeeding.
In terms of your original question, it depends. I know some students who earned perfect scores by memorising entire chunks of texts, which they would then adapt to the passage using a more specific variant of the technique I discussed earlier. This is rather painful though, and really, I wouldn't recommend it unless you were crazy about your study score.
Personally, I wrote about 3000 words of notes for both texts I wrote on (Emma and Hamlet), making sure that I had an interpretation on virtually every single aspect of the texts which might possibly come up. However, the stuff that I DID write was generally relatively broad, and adaptable - my modus operandi was to have a flexible idea of specific interpretations which I didn't necessarily need to know word-for-word, but which I could nevertheless churn out instantly in fresh and original ways off the top of my head. This basically resulted in me adapting pre-existing ideas to the slightly unexpected passages in the exams, with my last paragraph for Emma in particular being something that I had never ever written on before.