I see, thanks. Any reason why they're not represented in the same form?

In t5sp (zm) and t5mp, when I start a private match and write status to the console, it will return the same GUID for my player. Doing the same in t6zm however won't return the GUID but the XUID as far as I can tell. The column header claims it's a GUID, though. Shouldn't the GUIDs be the same across all games?