MIDI implies a basic format, certainly, but no more. Repeated phrases, for example, are usually sounded out directly, rather than using the equivalent of |: :| ; since there is no concept of a 'page' in MIDI any thoughts like 'where is the best place to put a page break', 'how many systems to a page' and so on simply don't apply. Although it is possible, I have very rarely seen the sort of overall flavour of the music in MIDI that is common on sheet music: 'Majestically', 'Soothingly' and so on. Signs like mp, ff and so on are directly represented in the volume of the notes, so don't exist as separate symbols. And so on.