Speed of light between a source and target moving wrt to each other

Passionflower
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How much experimental evidence is there that the speed of light stays c between a source and target moving wrt to each other?
 
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The idea that the speed of light might depend on the velocity of the source was known as emission theory. It was tested by the Alvager experiment, in which 6 GeV neutral pions were allowed to decay in flight: π0 → γ + γ. The photons were then timed over a flight path of about 30 m, and the result was that the velocity of the photons was within 10-4 of c.
 
Bill_K said:
The idea that the speed of light might depend on the velocity of the source was known as emission theory.

I'm wondering if that might be an over-generalization. Won't emission theory specifically be the case where the velocity of the emitting particle is added to the nominal propagation velocity?

Other theories might exist where the velocity of the source affects the local speed of light without necessarily adding linearly to the nominal propagation velocity c. If such effects are reciprocal in the sink then they may cancel leaving a perceived velocity c (which could indicate a deficiency for physics modeling the perceived effects in comparison to physics modeling the underlying effects).
 

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