How are vertex normals being calculated regarding object origin? There is simple uneven surface:



Its origin point is located where 3D cursor is. Once selected edge loop is extruded its vertex normals are expected to be as a continuation of connecting edge, like:



However they are shifted            and are oriented down:



If changing origin point they change their orientation. They get approximately desired orientation if origin point is snapped to 2 vertices of the edge loop not selected on the first screenshot.

Are vertex normals oriented regarding the origin point location ?
How to orient vertex normals of the mesh to be oriented as a continuation of adjacent edges ? (this could be useful for some cases like scaling along normals etc.)
To workaround this extrude faces of that surface to form a volume; faces will be extruded along their normals which have roughly the same orientation as vertex normals in this case (except for the corners where vector differs because of one additional orientation):



Then vectors are suitable for such tasks like scaling along normals as they roughly got desired orientation.
This is more a workaround as extrusion might not be convenient, but it's always possible to hide faces around mentioned and work only with those needed.