I had a similar "variables" problem when designing a choose-your-own-adventure book with my kids. I wanted your character to be able to reach the same pages but have state -- e.g. have a key or not have a key. I didn't want to have to duplicate pages with different state (which I kind of remember from old CYOA books -- there's be pages with almost the same thing, but now slightly different because you entered the room with a sword or whatever).

In the end, because it's a book and not a computer game, we could just ask the user: "If you have a key, turn to page 43..." and it just depends on the user being honest (or as honest as any reader of a CYOA book is, with nine fingers stuck between pages).

I assume there were similar books in the past that used the same mechanic -- maybe the Fighting Fantasy books? I forget.