Lost Enlightenment:

The violin concertos here are not the familiar pair in A minor and E. Bach composed a number of concertos for orchestral instruments and later transcribed them as keyboard concertos. Reversing Bach’s procedure, Wilfried Fischer has taken the harpsichord versions and from them has reconstructed the originals. BWV 1056 is a transposed transcription of the Keyboard Concerto in F minor (though New Grove identifies the outer movements as being from a lost oboe concerto). The D minor work is also usually heard in its keyboard adaptation. The concerto in C minor for two harpsichords appears in its original instrumentation for violin and oboe, the soloists here being perfectly balanced for clarity of line. It was Tovey who suggested that the A major concerto may have been intended for the oboe d’amore, an instrument pitched between the oboe proper and the cor anglais.