I assume from your response that you accept that I'm being truthful when I write that Apple hardware MacPro1,1 doesn't have a system-id (and it's IOPlatformUUID starts with zeros);
[apple:~] me% ioreg -l -p IODeviceTree | grep IOPlatformUUID
| "IOPlatformUUID" = "00000000-0000-1000-8000-0017F25951A8"
[apple:~] me%
The system-id is a construct of IntVar's modification of David Elliott's fake_efi.c, not of Apple's code, and IOPlatformUUID is derived from en0's MAC on some Apple hardware, and from something like uuidgen on other Apple hardware (?=alphanumeric);
MacPro1,1: 00000000-0000-1000-8000-???????????? (last 12 is en0's MAC)
MacPro2,1: 00000000-0000-1000-8000-???????????? (last 12 is en0's MAC)
MacPro3,1: ????????-????-????-????-???????????? (?)
MacPro4,1: ????????-????-????-????-???????????? (?)