why write the page numbers down? I don't think it would help, because they could just flip all the pages and find the words. It's only for convenience, but actually writting the page numbers on another notebook creates one more place where they could search. Besides, if you wrote down the page numbers (i.e 12 numbers), you could also write down the numbers of the words in the BIP-39 list (e.g. 291 for cattle, 103 for art etc).