C99 isn't a compiler version. It's a standard. Many versions of GCC, Clang and other compilers can compile C99 code. If you update your compiler from gcc 14.1 to gcc 14.2, both versions can still compile standard code.
There is also a very high level of backwards compatibility between versions of ISO C because there is a gigantic amount of code is updated if there is change. So such changes are done only for important reasons or after a very long deprecation period.
