Thank you @mudski.

Do you have a picture to illustrate GU1 and GU2?

The way I see it there is original GU pre-facelift (ranging from GU1, 2 and 3 between which I can't see any difference) and the GU post-facelift (from GU4 onwards) where the only difference I noticed is the rear bumper with the 3-piece with aluminum step or single piece all plastic. Ok, to be honest there is also black headlights and black taillights but that would be too cosmetic to me to be called a new version, as it is just a color change, not a facelift.