A panel of appeals court justices closely questioned Pennsylvania prosecutors Tuesday about whether Bill Cosby had been treated fairly at his sexual assault trial in 2018 when five other women were allowed to testify that they too had been similarly abused by the entertainer in encounters stretching back into the 1980s.

The hearing before Pennsylvania’s Supreme Court, the state’s highest court, was part of Mr. Cosby’s latest effort to overturn his conviction in the drugging and sexual assault of Andrea Constand at his home outside Philadelphia in 2004.

The decision by the trial judge to include the testimony by other so-called “prior bad acts” witnesses had been a key moment of the trial. But Mr. Cosby’s defense team has argued that the collective weight of the women’s accounts, which had never been the subject of criminal cases of their own, had unfairly tainted the jury.

“Mr. Cosby suffered unquantifiable prejudice,” a lawyer for Mr. Cosby, Jennifer Bonjean, said at the Tuesday hearing.

“The presumption of innocence just did not exist for him at that point,” she added.

Prosecutors from the Montgomery County district attorney’s office defended the decision during the 75-minute hearing, which was held virtually, arguing that the testimony of the other women established, as recognized under Pennsylvania law, a signature pattern of conduct by Mr. Cosby.

The inclusion of so-called “prior bad acts” testimony is rare, but in Pennsylvania, as in other states, it is allowed if, among other conditions, it demonstrates a signature pattern of abuse.

But some of the seven justices seemed unconvinced and questioned the prosecutors sharply about the inclusion of the other women.

Referring to the argument that the testimony established apattern, Justice Christine Donohue said, “Frankly, I don’t see it.”

Justice Max Baer said, “I tend to agree that this evidence was extremely prejudicial.”

At least three other justices questioned the reasoning for allowing in the testimony by Mr. Cosby’s other accusers.

Mr. Cosby’s conviction in April 2018 capped the precipitous downfall of one of the world’s best-known and most popular entertainers. It also offered a measure of closure to the dozens of women who for years had accused him of similar assaults. To many of those accusers, the verdict was a development that reflected that, going forward, the accounts of female accusers might be afforded greater weight and credibility by jurors.

Mr. Cosby, 83, is now serving a three- to 10-year sentence at SCI Phoenix, a maximum-security facility outside Philadelphia.

But since his conviction, Mr. Cosby, who denies his guilt and says any relationships were consensual, has fought to overturn the verdict, arguing that important decisions made by the trial judge, Steven T. O’Neill, of the Montgomery County Court of Common Pleas, had denied him a fair trial.

A lower appeals court, however, agreed with Judge O’Neill and upheld the conviction last December. But the Pennsylvania Supreme Court subsequently agreed to hear arguments on the judge’s decision to allow other women to testify. It also agreed to review Judge O’Neill’s decision to allow the trial to go ahead despite a former district attorney’s statement that he had once given Mr. Cosby his binding assurance that he would not be charged in the case.

The former district attorney said he had given Mr. Cosby the assurance to encourage him to testify in a civil case brought by Ms. Constand. In that testimony, Mr. Cosby acknowledged giving quaaludes to women he was pursuing for sex, and as part of the current appeal, the Supreme Court is considering whether the jury should have heard that testimony.

Any ruling by the appeals court to overturn the verdict would be by a majority vote and is not expected for several months.

Mr. Cosby’s case represented one of the most high-profile convictions to unfold in the aftermath of #MeToo. His team has argued that the trial judge was swept up by the fervor of the #MeToo movement, leading him to allow the testimony from the other women, although Ms. Bonjean did not cite that argument when appearing Tuesday.

Such testimony by other accusers played a part in the Harvey Weinstein case, where the testimony was sought to demonstrate a pattern of predatory behavior by Mr. Weinstein.

Mr. Cosby’s lawyers say the “prior bad acts” testimony should not have been allowed in his case because the accounts of the other women were too remote in time and too dissimilar to the case for which he was being tried. His defense team, for example, said that the relationship with Ms. Constand unfolded over several months, whereas the encounters with the other women took place in a much shorter period of time.

Prosecutors on Tuesday pushed back against any suggestion that the decades-old accounts should not have been admitted. Adrienne D. Jappe, an assistant district attorney, said the older encounters the women described had occurred in roughly the same time period and together showed a compelling pattern of behavior. “You don’t look at these in isolation,” she said.

Judge O’Neill allowed just one “prior bad acts” witness to testify at Mr. Cosby’s first trial in 2017, which ended with a hung jury. But at the 2018 retrial, in the face of opposition from Mr. Cosby’s lawyers who argued the women’s accounts would be prejudicial, Judge O’Neill allowed five accusers to testify along with Ms. Constand. Prosecutors had requested authority to introduce the accounts of 19 additional women, in total. (Dozens of women had come forward.) Prosecutors said the additional testimony was necessary to corroborate Ms. Constand’s account.

A spokeswoman for the Montgomery County district attorney’s office, Kate Delano, declined to comment after the hearing.

Andrew Wyatt, Mr. Cosby’s spokesman, said Mr. Cosby did not watch the proceeding but that he kept him informed.

“Mr. Cosby can’t watch anything because he’s 100 percent blind, due to glaucoma,” Mr. Wyatt said in an email on Monday. In addition, he said, Mr. Cosby has requested that no radio or television be placed in his cell. He said that Mr. Cosby does not want to make his incarceration “feel normal” and that ”outside distractions” have a tendency “to make one complacent.”

On Tuesday, he said that Mr. Cosby called him 20 minutes after the hearing for an update, and Mr. Cosby dictated a statement that Mr. Wyatt posted to Mr. Cosby’s social media.

In the posting, Mr. Cosby thanked his lawyer, family and supporters. “I hope and truly believe that justice will be done,” he wrote.