Dear folllowers,
Imagine you are in 1905, where experiments known today were not done.
Does aberration of light exist for a source horizontal to a moving frame?
Such a phenomenon (which mathematical reinterpretation should be done) wouldn't it explain c constancy in case of galilean addition of speed?
(The source being independant, every photon evolves in the detection frame where information is delayed relative to the real position giving c constant instead of galilean addition).