Apparently the recorders were really intense about this. We have a record of King Taejong complaining about a recorder who followed him on a hunt in disguise and another who eavesdropped on him behind a screen. No one was allowed to see the records, even the king (one king did and killed five men based on what was written there, after which they took greater care to ensure it would never happen again), and changing the content or disclosing it was a capital punishment. Even when there were rival political factions trying to influence the writers, they wrote down what was a revision and what wasn’t and kept an original version with no revisions in it.
They also made sure to back up their data. They made four copies of it, then when three copies were lost in the Imrim Wars they decided to make five more copies just in case. One copy was destroyed in a rebellion, another was partially damaged in an invasion, and Japan stole one copy during their occupation and moved it to Tokyo University, where it was mostly destroyed in the Kanto Earthquake (47 books remained and were returned to South Korea in 2006). Now the whole thing is digitized, free on the internet, and translated into modern Korean for all to see.
It took centuries of meticulous recorders, justifiably paranoid copiers, absolutely determined historians, and painstaking infrastructure for this joke to be possible. Happy 618th anniversary to the day King Taejong fell from his horse.