So it turns out that all the traingles from CAD geometry don't have smoothing groups assigned, even though the normals separated along the hard edges and unified on smooth edges. Soooo.... I had already unwrapped the mesh, so just before resetting all the normals I ran a script I found here by RenderHJS that assigned SGs…
Also you can always export a hi poly model and transfer/ borrow normal directions from it. I do so with model copy dynameshed in Zbrush to tiny polygons. Max doesn't have a native tool for normals transfer but there are 3d party scripts starting with normal theft . Or you can always do it with data transfer in Blender…