I recently finished reading "Gone Girl" and, although I enjoyed it, there is a part of the story that sounded kind of weird for me, and it kind of keeps bothering me.
Amy starts planning everything a year before "the day of". As part of her plan, she writes some diaries simulating diary entries which were supposed to be 6 years old. If there were a forensic way of determining the age of the diaries they could have known that Nick was telling the truth, even if the method was not very precise, the difference between 1 and 6 is huge.
In real life, would this be a plot hole or there is no way the police could find out such a thing?