The church denied the letter was a so-called "smoking gun," as described by some clerical sex abuse activists.
But attorneys for victims of pedophile priests say it may embolden more to come forward and could help one day lead to successful lawsuits against the Holy See itself.
Just last week, Jeffrey Anderson, the pre-eminent attorney for Catholic sex abuse victims in the U.S., opened a new office in London to handle the influx of cases coming to light because of last year's scandal in Europe.
Anderson, of St. Paul, Minn., told AOL News today that he has heard from even more victims since the letter was revealed Monday night in a documentary shown on the Irish TV network RTE.
"The letter is a strong piece of evidence that shows and demonstrates what we've claimed all along," Anderson said.
"It shows that the Vatican is in control and that it protects the reputation of the hierarchy over the well-being of children. It shows that all roads lead to Rome. More victims are feeling empowered so we're hearing from people from Australia to the U.K."
But Vatican spokesman the Rev. Federico Lombardi denied that the letter was proof that the Holy See told Irish bishops not to report clerical sex abuse to the police.
"That letter has been given biased treatment by some media outlets, who have presented it as proof of an instruction from the Vatican to cover up cases of sexual abuse of minors," Lombardi said today.
"It must be noted that the letter does not in any way suggest that national laws must not be followed."
The letter, reportedly leaked to RTE by an Irish bishop, appeared to warn Ireland's bishops not to report all suspected child-abuse cases to police. It seemed to reject a 1996 proposal by Irish bishops to outline a system of notifying police about pedophile priests in the wake of Ireland's first clerical abuse lawsuits.
That's not true, the church said. The letter was simply meant to make sure that Irish bishops followed canonical law and was not to protect pedophile priests.
"There's nothing in the letter that says do not obey the civil law," Jeffrey Lena, the U.S.-based attorney for the Vatican, told AOL News today.
Lena also issued a statement saying the letter had been "deeply misunderstood." He said the letter was intended to ensure that Irish bishops follow canonical law to the letter so pedophile priests could not get off on a technicality. He added that its actual meaning, therefore, was in "stark contrast" to how some media outlets portrayed it.
"You're going to see more and more attention focused on the Vatican and how to make it more accountable in these cases," he said.
Stack, who attempted to sue the Vatican in a key clerical sex abuse case in Canada years ago, said it's still very difficult to pin the Holy See down in court.
In fact, a long-running Kentucky case naming the Holy See as a defendant fell apart in August in large part because of a court ruling that recognized the Vatican's immunity.
"It's going to be extremely complicated because the Vatican is a sovereign state," Stack said. "If the Catholic Church was simply a worldwide religion, it would be easier to go after the head of it. But when you're dealing with issues of sovereignty and treaty rights and all that, it's complex. But within five or 10 years, you may start to see that inroads are being made."
Andrew Madden became the first Irish victim to go public in 1995 with the revelation that church officials paid him to stay silent after he told them the family priest had abused him for three years.
He took to Twitter today to decry the letter.
"It just confirms for me that the cover-up goes right to the heart of the Vatican," Madden told AOL News. "They've always tried to [say] it's a few rogue bishops that did it locally. I've never believed it. Strategies are identical all over."