Flight Delta Airlines DL9856 seems to be a generic code for substitution flights in replacement of normal flights that couldn’t be opered for technical problems.
On Feb 12 2015, DL9856 is a flight from Paris CDG to Atlanta, departure 0930 AM. I was booked on this flight due to cancellation of DL0083 the day before, same aircraft.
The aircraft appeared to have the same technical problem (motor engine) and couldn’t take off.
On the flight status history, this flight is not mentioned :
Flight should be mentioned for the day of February 12 2015 on a Paris CDG > Atlanta route, departure Paris CDG 09:30 AM and with the status cancelled.
If requested by Flightaware moderator, I am able to post a picture of a boarding pass to prove about this flight.