“In order to prove you’re a truth teller, you have to prove it happened,” said Joseph Cammarata, who represented seven Cosby accusers. “This is a direct way to get at the person who assaulted you.”

In Ms. Judd’s case, it could lead to a hearing over her account of visiting Mr. Weinstein’s room at the Peninsula Beverly Hills hotel one morning in late 1996 or early 1997, expecting a professional breakfast. She said that Mr. Weinstein, wearing a bathrobe, had requested to massage her or for her to watch him shower, and that she had refused.

Ms. Judd has argued that Miramax called her a “nightmare to work with” in retaliation for the hotel encounter. Miramax’s alleged conversation with Mr. Jackson occurred more than 20 years ago. The statute of limitations for a defamation claim in California is just one year, but the judge let the case go forward, saying that it was plausible that Ms. Judd would only learn about the conversation through Mr. Jackson’s 2017 interview. (The judge threw out Ms. Judd’s sexual harassment claim, saying it did not fall within the scope of California law.)

Mr. Weinstein has not directly disputed the allegation that Miramax said Ms. Judd was a “nightmare to work with” but has argued that his attempts to land her major acting roles later on showed that he was not trying to hinder her career. He has denied having any nonconsensual sexual encounters, including with the two women at the center of his rape trial in Manhattan. On Monday, prosecutors in Los Angeles announced that he had been charged with rape and sexual battery in connection with encounters with two women there.

Compared with some other countries, in the United States a defamation case is relatively difficult to win, because of a standard set by the Supreme Court to protect freedom of the press. If the plaintiff is a public figure, as many are, he or she must prove the statement was both false and made with “reckless disregard” for whether it was true.

In countries without the same high bar, including China, Australia and France, men have won high-profile defamation cases against women or news outlets that published their stories.