Have you forgotten that in addition to Mansouri-Sexl I provided this credible reference very early in this discussion? Y.Z. Zhang,
Special relativity and its experimental foundations, (1997);
http://www.worldscibooks.com/physics/3180.html
In the preface he says this: "The key point in Einstein's theory is the postulate concerning the constancy of the (one-way) velocity of light, which contradicts the classical (nonrelativistic) addition law of velocities. The postulate is needed only for constructing well-defined inertial frames of reference or, in other words, only for synchronizing clocks (i.e., defining simultaneity). It is not possible to test the one-way velocity of light because another independent method of clock synchronization has not yet been found...Of course one could use the experiments to yield limits on the parameters in Robertson's transformations but not on the directional parameter q in Edwards' and MS' theories."
On the back cover Zhang says this: "...In particular, the discussions indicate that the one-way speed of light is not observable in the present laboratories...In the third part, variant types of experiments performed up to now are analyzed and compared to the predictions of special relativity. The analyses show that the experiments are tests of the two-way velocity, but not of the one-way velocity, of light."
On page 10 he says: "We want to stress here that only the two-way speed, but not the one-way speed, of light has been already measured in the experimental measurements, and hence the isotropy of the one-way velocity of light is just a postulate...We shall see from Chap. 6 that a more general postulate, a choice of the anisotropy of the one-way velocity of light, together with the principle of relativity, would give the same physical predictions as Einstein's theory of special relativity."