"If there was one mention of it in something Riddle could find, there's bound to be more that he didn't." Hermione didn't quite believe that, though. She imagined that Riddle would have tried to look through everything, just the way they were doing now, after he'd found one taste of the information. And he hadn't been able to find more, which was why he'd gone on to asking others.
It was also vaguely creepy to think that Riddle had likely touched all of the books she was touching now, but not enough to make her stop. Surely, he wouldn't have been able to look through everything before his patience gave out.