[Physicist]

Can we check the estimate of the charge by looking at curvature of the flight path, the mass, and the applied B field?

I don't know whether we have a good estimate of the magnetic field out there. If my explanation is correct, it may turn out that it was rejected early on because of mistaken assumptions about the size of the magnetic field and the net charge on the probes.

[NicknamedBob]

"... looking at curvature of the flight path..."

This seems to be inherently an unlikely possibility. Wouldn't any such deviation or curvature from its path be a great deal easier to detect than its Doppler shift?

What about an uncalculated effect of cold gas mass on slowing the craft gravitaionally?(As for example, a rather depleted "solar wind"?)

That would seem to make the gravity field a little more steep as it went.