Thank you for asking @rskedgell.   Road positions were considerably based on gps track + satellite imagery.  While many of the building positions were based on satellite imagery of the area during building, some was based on imagery from the council and the property developer.  I now see the council 'map' site is indeed based on OS data, so some of the exact building locations may not be 'safe' on that basis.  What would be the correct way to undo / revert the changeset or otherwise remove unsafe changes?