The story of the first movement’s origins has all the makings of a whodunnit: during Bach’s lifetime, the score was neatly and systematically severed from a larger sheet (containing the Harpsichord Concerto BWV 1062) after bar 62. But why and by whom? Though a replacement sheet must have existed, it has been irretrievably lost. Thus the missing ca. 46 bars have been reconstructed with varying degrees of accuracy in all previous editions, and sometimes the movement was even entirely omitted. Bart...