Caseback is weird without the modelnumber and the serial number, also, if you have a version from outside the EU it says on top: "Stainless Steel and 18k Gold", but nothing on this one. Either it has all been polished out (not likely) or replaced. There might have been a personal inscription on it of a name or text, and replaced by the next owner. I have seen totally blank casebacks before on several watches, most of them 6000 models, and always wondered why, but this could be an explanation.