There are some things you need to be aware of when working with any NURBS data imported in max.
First off, body objects' face shading is based on explicit normals (they are defined by the NURBS data already, they're not not based on max internal smoothing groups like any other model you create in max), once you invalidate them there's no way back. If you attempt to generate normals through smoothing groups they will never look as clean as the original explicit normals, this will usually produce a lot of artifacts.
If you need to convert to meshes, make sure to convert to editable meshes, editable polys may corrupt explicit normals (they may work fine but sometimes they just don't). Be aware that vertices are always unwelded in converted meshes, to weld them use either:
- the weld & smooth option in the body object (mostly works, sometimes produces artifacts) and then convert to editable mesh
- convert to editable mesh first, then use the ProOptimizer modifier, leave the face count at 100%, check 'Weld Vertices' with a tiny threshold to keep all vertices and check 'Keep Normals'. Convert to editable mesh again, vertices should now be welded.
Some modifiers in max will corrupt explicit normals, you'll see it when it happens, in this case avoid using these modifiers.
Detaching elements from or attaching objects to these meshes will definitely corrupt normals.
If you need to detach elements, make a copy of the object, and delete the elements you don't need. On the copy delete the inverse selection. I you need more elements detached, then it's a bit of manual work.
If you need to attach to these meshes, avoid using the attach command from the editable mesh object and rather use the collapse command from the utilities panel, this will not invalidate normals.
Some of these problems have been addressed in the latter max versions, what I suggest is based on max 2012 but it seems similar problems still persist in max 2014, not sure about 2015 and 2016. If you see related artifacts with your normal workflow then you have some workarounds at least.
Keeping NURBS data as body objects without converting them is also completely valid. There's no need to convert as long as you don't need to modify the resulting mesh. Only make sure that the render mesh is set to use the viewport mesh to avoid different results between the viewport and rendering.
