Combat archive 9 downgrades Erich Rudorffer puzzled

[BOBC]

Hi
Wikipedia:-
He stayed there until 7 January 1940, one day later, Rudorffer, now an Oberfeldwebel (staff sergeant), was posted to the 2. Staffel (2nd squadron) of Jagdgeschwader 2 "Richthofen" (JG 2—2nd Fighter Wing), named after the World War I fighter ace Manfred von Richthofen.[2]

Combat Archive 9 p5 1 Sept 1940 1/JG2 Fw Erich Rudorffer. Spitfire Dover

Surely he didnt go down a grade when moving to 1 staffel ? Can anyone confirm he did move to 1 staffel JG2 in fact or was this a temporary move ?

What book or website has all the movements and ranks of all the Luftwaffe Pilots in the Battle of Britain ?

Thanks

BOBC