for the missing curves after
_Silhouette, you might check your model for naked edges using
_ShowEdges, bad surfaces using
_ExtractBadSrf and in areas where you get multiple curves, extract the surface and check if they have multiple knots using
You may check your document unit and angle tolerances too. If they are set too coarse,
_Silhouette sometimes makes problems. To go deeper you might provide the model for closer inspection.
Appart from all this, there is only the
_DraftAnglePoint command which might help to get the points which form the curve you search for. To find more about it, run the command and press F1