I went and worked on this for a while, and it looks like what is going on is that Gruffudd had two daughters named Nest, by two different wives, and they have two different birth years, and one is married to one of the husbands, and the other to the other one.
I will pull all this together in the morning, and add references to the profiles and the discussion.
Ok, Sharon Doubell -- I have untangled Gruffudd's wives and children, and added in notes and sources and explanations, and moved everybody around.
The basic problem is that the genealogy right at this point is being constructed both from the medieval genealogies and the histories, and it gets Complicated.
But I think Darrell Wolcott has made pretty good sense of it, so we went with that.
There is now the Nest you linked to for this discussion, AND her half-sister: Nest (1) verch Gruffudd