From the help File:
Interoperability Between Versions
This topic describes the behavior when an AutoCAD Civil 3D 2017 drawing is opened in prior versions of AutoCAD Civil 3D.
Objects in a drawing saved in AutoCAD Civil 3D 2017 are available only as proxies when the drawing is opened in a prior version of the software.
Within AutoCAD Civil 3D 2017, set the PROXYGRAPHICS drawing setting to 1 to save the graphics with the drawing, otherwise a bounding box is displayed where the object is located when the drawing is opened in a prior version of the software.
Notice when you open an older version file:
Civil 3D 2016, 15, & 14 are backward compatible to
13. Versions prior to 2013 are not backwards compatible