In post 12 I have explained why the speed of light is not constant. In posts 9 and 15 I have explained why Einstein’s Equivalent Principle is out of date as he did not take account of the difference between endogenous and exogenous processes. The General Theory of Relativity is based on the premises of a constant speed of light (see also post 1) and the Equivalent Principle. The speed of light not being constant and the Equivalent Principle being out of date, what does that mean for the concept of relativity in cosmological sense? This question can be answered as follows.
Nothing can go faster than the speed of light ceteris paribus.
There is light here and there is light there, because there is light everywhere.
The speed of light can be higher here than the speed of light there or the speed of light there can be higher than the speed of light here. Therefore something can go faster here than the speed of light there or something can go faster there than the speed of light here.
This is what I call cosmological relativity.