The significance of the flyby anomaly (which has been observed at up to 13mm/s
.. which is still only 0.000094628% of the craft's speed, assuming the previous poster's quoted speed is correct.
And let's not forget it's the 'RE model', i.e. everything we currently know about planetary masses, the theory of gravitation, which predicts varying gravitational attraction between the planet and the spacecraft depending on the distance, not forgetting the difficulty of that attraction changing continuously as they change relative positions, etc. I was actually quite surprised they could predict to anything like that accuracy.
And, not meaning to be impolite or uncivil, FE still can't predict the seasons, nor the movements of stars. By 'predict' I mean, taking the theory plus observations and a bunch of mathematics that tells us e.g. where any star will be at a given time, exactly when the season will be etc.