OS is certainly not definitive, although they are very good. 1) There is a disclaimer on OS maps that says so 2) The definitive map is held by local councils

OS is certainly not definitive, although they are very good. 1) There is a disclaimer on OS maps that says so 2) The definitive map is held by local councils 3) A right of way can exist without registration, and is created through use. The medieval alley ways in my local town only recently became registered after hundreds of years of use. They were always rights of way and you could not have prevented their use. 4) There is a right to roam in Scotland and a limited right to some land in England and Wales under CROW Act.