There are many reasons. In traditional settings, content was provided by teachers and learners „recorded” them by taking notes (early medieval university setting). That basic configuration evolved by official notes by teachers themselves, and official notes could reach the form of publications. But publications were already made by professionals, who dealt with the hand-written manuscripts. Still in this form of mediatisation of content, teachers (authors) had to make some further decisions about the structure of their publications and had to check the draft. (See the art of hand written editing marks: http://amundsenhs.org/ourpages/auto/2008/8/28/1219939376443/Common Proofreading _ Editing Marks.pdf). Later when pictures, audio and motion pictures helped education (either during classes or after), technicians and professional media people (groups) produced audio, visual or even audio-visual learning media. All media from print through audio till educational films had their own industry, industry standards, formats, time indications, volume indications, editing and cut archiving protocol. Till the computer-era this content publication was made by different analogue methods (typesetting, tape recording, celluloid film recording).
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