I apologize if this has been posted before but I searched and wasn't able to find what I was looking for. I have seen multiple pictures of the nose bridge on the old XX Twenty frames (O-matter not metal), and some of them only have the "XX" and some of them also have the word "Twenty" stamped above the XX. Is this something that changed year to year as they were produced or is it a sign of possible fakes? If its something that changed year to year, is there an approximate way to date each version of the stamp to know how old the frames are? Thanks in advance for any help.