The Flightaware track log for DLH469 shows a maximum altitude deviation of 300 feet from FL370 about an hour into the flight, with about 2 data points per minute recorded. At about 90 minutes into the flight when the FAA and Lufthansa reported the severe turbulence event occurred, altitude deviation is no more than 25 feet. AvHerald reports the severe turbulence occurred 150nm NW of KIAD, which is about 40 minutes later in the flight and coincides with the aircraft altering course and diverting to KIAD.