Beverly Young Nelson claims she was a 16-year-old waitress when Moore groped her and tried to force her to perform a sex act in his vehicle.
Nelson, who says she voted for Trump, worries that partisan politics has eclipsed moral judgment.
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".
Nelson's attorney, Gloria Allred, maintains that the rest of the inscription is real and that it is proof that Nelson knew Moore, who Nelson said groped her in his vehicle after offering her a ride home. "And he signed it ' Roy Moore D.A'".
Allred added: "We did not ask the expert to examine the printing after the cursive writing and signature, because Beverly indicates that she added that to remind herself of who Roy Moore was and where and when Mr. Moore signed her yearbook".
Besides examining the yearbook, Allred said Anthony also authenticated Moore's handwriting on a graduation card that Debbie Wesson Gibson said she received from Moore. Nelson offered the yearbook signature as evidence that Moore knew her and was, according to Nelson, a regular customer at the restaurant where she worked when she was 16.
She admitted adding the date and location under Moore's signature, despite her attorney Gloria Allred's earlier claim that the Republican candidate wrote it all.More news: Flu season could be the worst in almost a decade
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Allred said she retained forensic handwriting expert Arthur Anthony to examine the inscription by comparing Moore's "known standard handwriting and signature to the entry in Beverly's yearbook".
Beverly Nelson is fighting for credibility Friday.
Several Moore supporters have claimed that Ms Nelson may have committed fraud.
Moore only wrote the first part of that message up to his signature, she said.
Moore has denied the accusations of pedophilia and sexual harassment, and on Friday, he tweeted, "Now she herself admits to lying". Her new admission about date and place, however, isn't playing well online.
He said Doug Jones will be "completely controlled" by the Democrats and declared that they need someone in that Senate seat who will support his agenda.
Allred said today that a handwriting expert determined that the signature in the yearbook was authentic. "They're malicious. Specifically, I do not know any of these women, nor have I ever engaged in sexual misconduct with any woman". Moore, who has not appeared in public since a rally Tuesday with former White House strategist Stephen Bannon, did not attend the news conference.