When you have only the Doppler shifts, the only thing you know is the speed of the aircraft RELATIVE TO the satellite. You don't know the distance between the two, and nor do you know precisely the track of the aircraft.
Doppler shift gives you radial speed relative to the satellite. ie, a hypothetical plane flying a curved track along the 40 degree contour would have zero doppler shift (and constant ping time.) Nobody thinks a curved track was flown by 9M-MRO.
The combination of changing ping time and doppler gives further information, but does not appear to be sufficient to identify a single location without assumptions about speed, fuel, and altitude.
It's all going into a mathematical model. When some of the assumptions (variables in the equation) change, the results change.