Christian David Graff worked as organist at Kirche St. Ulrich und Levin in Magdeburg from 1719 until his death in 1774. He was a pupil of Johann Bernhard Bach (a cousin of J.S. Bach). In the past Graff was considered a pupil from J.S. Bach, but that isn't true, probably the cause of a confusion between J.S. and J.B. Bach.
Christian David Graff played at a Schnitger organ in Magdeburg. So the beautiful sample set of the Schnitger organ in Steinkirchen was an obvious choice.