The gaps are on the standard library side: clang libc++ has fallen behind a bit on conformance, but you can use libstdc++ on clang as well (and it is the default for example on Linux). MSVC lags on C conformance, which is known not to be primary concern for MS (but still miles better than what it used to be).
In any cases these tables only help up to a point, even green cells often hide bugs and conformance divergences.
Still for most straightforward code compliance across compilers is very good and significantly better than the dark ages of two decades ago.
