Down through the years many different techniques have become available for recording history. This can be seen from the early days of the Bible. Different authors had a hand in recording the information. Many of the books are unknown. It has taken years and many different tools to get to the point that we are at today. Fortunately, the methods that were used preserved a good portion records and documents.
During the times of slavery and early presidents there no computers. There were no official post office systems during these days.You can find a quick rundown here Mail was delivered through handwritten methods. This was, of course, when handing writing was available. Lots of people could not read or interpret messages.
Over time more people learned about reading and writing. There were still others that learned through symbols. This goes back to ancient time of hieroglyphics. Lots of historians would have to get together on the translation of many different ancient temples or tombs. The writing of the walls of these areas would come after the Bible, but before words were set to paper.
History would later become recorded on electronic machines for voice. This would later be followed by the more popular electronic text documents.