I have a number of problems with your post.
1. No real problems with this, but still, it holds no support for your arguement.
2. Evidence can be destoried. If someone was determined enough, it is probable that he could destory all evidence of such an event. And this was much more true in Pre- to Early-Modern times. They lacked a vast majority of tech we have today. Perhaps far more then you think.
3. You also do not seem to understand Human nature. I say again, would you rather be seen as an Asshole or a Hero in history? Not just for some time, but forever. You also seem to not understand how far history goes back. The Roman Empire Existed somewhere around 3000 years ago. We still know a majority of events about them, such as there Conquests, Leaders, and Culture. We also still know and hate the people who were Assholes among them, and we are not going to forget the Roman Empire any time soon.
4. But everyone else will think that it was their harvest report, and since it was nothing of importance to most people, it is not really investgated. And when someone comes along wanting to record the Harvest reports, guess what they will get? As a hint, I will just say that the Ruler may not be so eager to release the truth, and telling that world that he had lied.
5. You also misunderstand how things back then worked. There was no TV News station, there were no Daily Papers, there were also no civil rights. Another thing is that there were not many historians who wrote History Books, because getting enough information could take Months, Years, even Decades! Combined with the fact that everything was handwritten, and you have not many people willing to take on the task. Rulers could however help, by providing funding and such, as long as you left out some certain pecies of information...
And even if you wrote a history book without any help back then, you still have to deal with a Nation not being so happy with what you provided. Fastforward a few decades, and you have someone wanting to write another history book, but all you have is what the last man wrote into the books. Given that they were funded or "encouraged" to leave out info by another nation, all you would have to work off of is false info.
6. History matters far more then how you make it sound. Knowing the past will allow us to learn from our mistakes, and help us preditic the future. If we threw away history like it was nothing, then we would have people making the same mistakes again and again, and maybe even throw another Hitler our way.