It's important to note that unlike Linux, NT system call numbers are not stable. That's a very good thing --- it effectively forces all system calls to go through ntdll, which can coordinate closely with userspace in interesting ways. It's as if NT's "vdso" covered all interaction with the kernel.

For example, NT has no native 32-bit ABI like Linux does. Instead, userspace translates 32-bit to 64-bit system calls, handling the switch from long and back to long mode transparently. This elegant approach is possible because applications never make system calls directly.