About Using Contour Data in Surfaces
Contours are graphical illustrations of surface elevation changes. You can create a surface from contours drawn as 2D or 3D polylines where each unique polyline contains points that are all at the same elevation.
About Supplementing Missing Contour Information
When you create a model from contours and then generate contours from this model, in some cases, AutoCAD Civil 3D may not generate the same set of contours.