Ok, so I've decided eventually to visit Punch for the first time and ask him for his service because recently I've been finally able to finish my Ironmight Plate Shield - and it's my only 5* shield that hadn't got any UV along the way (I was more lucky with other 5*).
And I got Increased Normal Defence: High
According to bars Ironmight Plate Shield already has max Normal Defence so there's no visible difference in stats.
But as I know that bars lie I have to ask if anybody noticed a difference between Ironmight Plate Shield with increased Normal Defence and regular one?!
Or is Punch trolling me?
I do not know the answer, but I can tell you something.
You know how wearing one piece of gear will make your total defences one half of the defense per piece?
Well if you wear one piece of Ancient Plate and one piece of Proto gear, the normal bar is almost filled.
So it goes beyond the bar.
Regardless of knowing that, I cannot answer your question fully.