[adrian_b]

The general relativity theory was not about gaps or corner cases of special relativity. It was about extending the theory outside its domain of applicability.

The theory of special relativity showed how to transform the physical quantities between inertial reference systems, i.e. systems where Newton's law of inertia is true. The relative velocity between the origins of such systems must be constant and there must be no relative rotational movement between them.

The theory of special relativity was not applicable to non-inertial reference systems, like one that has an accelerated motion relative to an inertial system.

Einstein's quest has been to find the transformation relations for this more general case. Together with the theory of the stimulated emission of radiation (1917), this has been the most original part of Einstein's work, because the previous transformations of the special relativity had been discovered before Einstein, he had just given a new explanation for them.

The only intuition related to general relativity was the guiding principle that whatever transformations will be found they must lead to indistinguishable local behavior of the forces of gravity vs. the forces of inertia.