Precision of tube tunnel locations on map

I have a casual interest in the finding the exact routes that tube/subway tunnels take through London. The routes on openstreetmap are the most detailed that I have seen. Some of the details of the routes are consistent with other information that I have come across. However, I did notice that the route of the Victoria line between Highbury & Islington and Kings Cross doesn’t pass through Gibson Square. I understand that there is a ventilation shaft for the tunnels in that square so I had always assumed that the tunnels run directly underneath there (but I don’t know this for sure). So I’m trying to determine whether the openstreetmap tunnel lines are only approximate or whether the ventilation shaft may not be directly above the tunnels and instead is connected through a non-vertical shaft to the tunnels. Does anyone know where the data for the subway tunnel locations on openstreetmap comes from and how precise/accurate it is?

Thanks for any help!