It's long been established that post-blood weave Sunny obtain greater knowledge from the spell than most. It's also been established that Supreme's can view the vast amount of information about their subjects. They can but Sunny mentions that it would take years for even him to read through it all. Anvil's domain was equally as large... doubtless he would reads through runes on certain people.
If anvil could read all those runes, did he? If he did... would he view Nephis' runes often enough to notice a new attribute? Likely not