The Windows runtime is backwards compatible, so there are no breaking changes in WinMD files. You should be able to just generate a module for the latest available version of Windows.WinMD.
Attempting to call functions which don't exist on the OS you are using should just result in E_NOINTERFACE being surfaced by this projection.
Attempting to call functions which don't exist on the OS you are using should just result in E_NOINTERFACE being surfaced by this projection.