No, the opposite is the case. There are not many letters of Johann Sebastian Bach at all still existing. There are two or three, may be four, which are written by hand which still exist and only one is filled with personal content. If we compare that with the correspondence which is left from other famous folks in music, science and politics it's a meager, really meager legacy.
And that is the reason, why it's not much known about Johann Sebastian Bach, about the "private" Johann Sebastian Bach. If you just read what Bach wrote in his famous letter to school friend George Erdmann about the depressing time in Leipzig, you may assume how much more the world would know about the composer today, if only Bach had written more letters or if more of the letters he might have been written would still be existing.
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