The MIDI samples are the 'mockups' of the track before being recorded with the orchestra and choir. In this set of recordings you can hear difference between the fake and real orchestra.
Note that the MIDI samples are rough mixes, i.e. not mixed/mastered. The real orchestral recordings are final mixes.
Checkout my mockup using MIDI samples of the theme to The Pacific (TV Series). This is using strings from a sample library, recorded in Cubase: https://youtu.be/QNJ3ABiZZdg
Composed by Steve Burke