It won't say guaranteed if the room doesn't have a choice. If you book a king suite, you should get a king suite. It is only rooms that say "or" that the guarantee affects. If you are plat, and your preference is entered, that guaranteed bit should show in the reservation for an "or" room types. It is in all of ours.

Orca, if you click on that last reservation

Marriott
Room(s)
Guest room, 1 Queen or 2 Twin/Single Bed(s)

And you click on change reservation, then click on "change room preferences" do you have the ability to select anything? And if you save it, does it now show guaranteed?