""""""""""Every good Catmull Clark Subdivision Surface implementation with Edge Weighting gives you perfect visual continuity in reflections.
The mushyness is countered by the edge-weighting. """"""""""

Catmull clark is "trying" to give you C2, though it can still result in C1 at extraordinary vertices. It does this by melting everything down to try that average. Repeated subs can get close. The "perfect VISUAL curvature" result just means you "cant see the difference".

I was thrown by the request being "G3", or even "G2". There's is a difference.

"""""""""Since I come from the polygon-world originally, I'm always amazed how much effort and money are needed to get something similar in NURBS"""""""""

That's because the NURBS are actually perfect, and "DO" represent that. It's much easier to kindof "average everything down" to be somewhat close........

But like Michael points out, YOU cant really see the difference.

But there is a need in very specialized situations, where those values cant just be "moved around"........