I'm not claiming that anything that's darker is something that's added, far from it. If this is done in more than one pass, there would be many places where the ink would match (the EVA-l on the second-last line looks like it may have been reinked).
I'm not claiming every letter of a particular kind (or a particular couplet) has been added either.
What I'm saying is look at it closely, in the zoom window, and sit back in your chair. There is a pattern here that occurs on a number of pages that says something different from linear writing is happening on at least some of the pages.