Simple....analysis of the inks...
Ball point ink 40 years ago is different from the ink used today.
Not only would an analysis of the inks be pertinent, but an analysis of Nelson’s handwriting. The implication now is that she added the notes back in high school. Handwriting changes over time. I recognize my handwriting from back in the day as mine, but I don’t think I would be capable of faking my own handwriting from decades ago. I doubt that Nelson’s added notes look like they did on the yearbooks she signed of her classmates, or where she signed her own name on her yearbook. I expect that even as she attempted to fake the autograph and notes, they will look suspiciously like her own current handwriting.