I have collected some GPS traces to check some of the shifts. For instance, there is an open oval at the centre of Saltdean that was was previously about 20 metres off from Bing and OS. I have driven around it to check my adjusted positions with GPS and was pleased with the correlation. Walking in urban canyons gives random GPS but walking down the middle of suburban roads (you often have to anyway because cars are parked on the footpaths) seems consistent. A lot of my changes to roads have been to correct shape and layout as much as position.