Issue generating MacPro7,1 serials - incorrect length

[1337GameDev]

I have attempted to generate dozens of MacPro7,1 serials, and noticed NONE are the correct length (if I go back into GENSMBIOS it tells me this when looking at my current SMBIOS data).

Plugging serials into the Apple check coverage page yields that it cannot check the serial (as it's invalid for that model and not the right length).

I also noticed that sometimes it generates the same serial over and over.

Is there any special inputs for MacPro7,1 (such as year/country) to generate the serials correctly?

Is there a bug, or am I doing it incorrectly?