Frood, just to talk with you, to define the number of polygons needed to well render a surface I always consider the border, I mean the silhouette of the surface, when it seems to be continuous it's ok. The shader has to do the rest. I also have to consider the total amount of poly in the scene, to have a "usable" scene.
We can talk one live about the meaning of high poly, and of course if I'm rendering a single object of course I can exaggerate with polygons, but in a regular set, with a lot of objects, I have to consider everything. Just yesterday I was talk with a friend, his "render boys" have create an exterior scene to be animated, with so much polygons, and it takes about 1 hour per frame!!!! He was killing them....I've stopped him just in time! ;)
Btw, someone has moved this tread in Resolved bug, but sorry, IMHO it remains a bug.
Take care, and thanks for your support.
PS: I'm curious, how many poly has got the highpoly teapot in
https://coronarenderer.freshdesk.com/support/solutions/articles/5000516258 ??...