One of the women accusing Senate candidate Roy Moore of sexual assault says she altered a piece of evidence proving a connection between the two people.
Ms Nelson's legal team say they hired a handwriting expert, who they claim has verified Mr Moore's signature in the book as genuine.
President Donald Trump jumped on the development during a boisterous campaign-style rally Friday night in Pensacola, Florida - just about 20 miles from the Alabama border - asking his audience if they had seen what happened as he plugged Moore's candidacy.
'Maybe, you know, he could be doing this still.
"The truth is out there, and until she releases the yearbook, all we know is that they are not telling the truth", Phillip Jauregui, a lawyer for the Moore campaign, said at a brief news conference.
This is a developing story. Against all odds, Moore has weathered sexual misconduct allegations while applying the same unorthodox playbook that many political operatives said wouldn't work for anyone but Trump.
Moore pounced on the comments to discredit Nelson's accusations against him, retweeting a Fox News headline saying Nelson "admits she forged" part of the yearbook note.
In one ad, Moore says the same "Washington insiders" who tried to stop Trump are also trying to stop him.
At a subsequent news conference, Nelson's lawyer, Gloria Allred, released the findings of a handwriting analyst who concluded that the signature on the yearbook inscription did indeed belong to Roy Moore.
Moore has repeatedly denied her allegation, as well as those from the eight other women who have accused him of sexual assault and misconduct.
The 70-year-old Moore, in a tight race against Democrat Doug Jones, tweeted his thanks to Trump for the endorsement..
The Moore campaign took no questions from reporters. "He wrote in my yearbook as follows: 'To a sweeter more attractive girl, I could not say Merry Christmas, Christmas, 1977, Love, Roy Moore, Olde Hickory House".
"We did not ask the expert to examine the printing after the cursive writing and signature", Allred said Friday.
Allred retained Georgia-based handwriting expert Arthur Anthony to assess the yearbook signature and cross-examine it with copies and originals of Moore's signature on other documents. Moore was an assistant district attorney in Etowah County at the time, so it was assumed that Moore added that designation after his name.
The Moore campaign previously attacked the credibility of Nelson's account by pointing out the difference in writing styles in the inscription.
"We are very transparent", Allred said. "Who does that?" she continued. "We look forward to learning if Alabama voters will believe Moore's accusers or ignore the evidence presented to them".