  Recent studies of spacetime anisotropy in the context of local Lorentz
invariance (LLI) based on classical Michelson-Morley experiments, as well
Kennedy-Thorndyke tests, pointed out the existence of terms first order in v/c
and of angular signatures independent of v. This contribution replaces the
Lorentz symmetry by a velocity gauge transformation following an argument
centred on observability. Results show even and odd order terms and indicate
that motion is always underestimated in the spatiotemporal platform. Though LLI
is not recovered in exact special relativistic terms, the alternative looks
compatible with the relational aspects of general relativity (GR) with variable
speed of light models as well a nonzero photon mass. This raises the hypothesis
that Einstein equivalence principle, and consequently LLI, is a cornerstone of
GR, but not necessarily a fundamental one of SR
