The winsock.def file lists the ordinals defined for the Windows Sockets APIs. In addition to the ordinal values listed, all ordinals 999 and below are reserved for future Windows Sockets use. It may be convenient for a Windows Sockets implementation to export additional, private interfaces from the Windows Sockets DLL. This is perfectly acceptable, as long as the ordinals for these exports are above 1000. Note that any application that uses a particular Windows Sockets DLL's private APIs will most likely not work on any other vendor's Windows Sockets implementation. Only the APIs defined in this document are guaranteed to be present in every Windows Sockets implementation.
If an application uses private interfaces of a particular vendor's Windows Sockets DLL, it is recommended that the DLL not be statically linked with the application but rather dynamically loaded with the Windows routines LoadLibrary() and GetProcAddress(). This allows the application to give an informative error message if it is run on a system with a Windows Sockets DLL that does not support the same set of extended functionality.