I was so pleased to hear that the cock was a later addition. I feel a tiny bit of national pride to know that my ancestors, seeing the Cerne Giant, thought "you know what that needs? A big old stiffie."
I've read that the dick had originally been sized more proportionately to the figure, but at some point it was merged with a large circular belly button, increasing its size/length.
I wonder whether that is the result the article is referring to, or whether there was an initial project to add a penis to the figure, followed by a distinct "this penis needs to be longer" revision later on.