I found a trap street! Comparing two editions of the Oxford A-Z street map, as you do, I spotted something had changed between 2000 and 2005 (apart from the typeface):
On the left, at the end of Beaumont Buildings, the earlier map shows a cul-de-sac labelled GOY CL. It was the strange name that made me notice it first - even allowing for the cryptic abbreviations of crowded maps, "Goy Close" seemed unlikely. "Godfrey Close" perhaps? But there was no entry in the index.
Just to be sure, I went to the end of the street and took this photo. Fortunately, despite being central Oxford, this is a back street off a back street, so no one's likely to be confused by the invention.