The thing about Mastery of an Art or even a Fighting system is that Mastery is the exact opposite of "Playing the music exactly as he wrote it." By default, you cannot master a skill without evolving. Even Bach didn't always play exactly as he wrote it. Word on the street has it that Bach was known for his improvisational skills and creativity. If someone describes you like this then you probably aren't lack the desire to do something exactly the same everytime.if you're playing Bach, you're supposed to play it exact every time.
If you are playing Bach and wanted to know how Bach Played the music then you play it exactly as he wrote it. But there are examples of Bach being played differently than he wrote it.
Example:
MC Fioti: His hit "Bum Bum Tam Tam" samples Bach's Partita in A minor for solo flute.
Eminem: In his song "Brainless," you can hear the fugue subject from Bach's Toccata and Fugue in D minor.
Busdriver: His track "Imaginary Places" samples Bach's Minuet and Badinerie from Orchestral Suite No. 2 in B.
The value of Bach is not that you "Play it the exactly every time." The value is that his music is still relevant today and this is how one's Martial Arts should be throughout time.