I provide a library with its header files to a user.

I often release new versions, minors and majors.

Sometimes the user still uses an old version of the header files and somehow he still can link the shared library against it.

Changes are made internally and on the API but on things he doesn’t seem to use, therefore I believe the linker still thinks it’s valid.

How can I version so that I’m 100% sure the user will use the correct header files with the library?

I’m not 100% sure the problem is this one, but it’s just a question.