Thee Land Registry property boundaries would seem to support  confusedbuffalo's idea. (See https://osmuk.org/cadastral-parcels/ for how to show them in OSM editors.)

So presumably the building under the note marker is actually 27A Victoria Avenue, while the building to the north (currently tagged as 5 Sandringham Close) is actually a semi containing 5 and 6 Sandringham Close.