And we've learned that this secrecy was invoked for 10 additional years after the victim reached the age of 18, under thread of excommunication.
Both of these statements are false.
The "10 additional years after the victim reached age 18" apparently refers to then-Cardinal Ratzinger extending the canonical statute of limitations on reporting abusers, thus making it easier for the church to prosecute them, rather than harder.
That is not why “papal secrecy “ is invoked. RC apologists can say that till the cows come home, but it won’t make it true.
People are not stupid. “Papal secrecy” means just what it sounds like it means. It means keep your mouth shut or you’re out of the church.
And Ratzinger’s letter has been posted many times. It says what it says...
http://www.bishop-accountability.org/resources/resource-files/churchdocs/EpistulaEnglish.htm
Don’t bother he knows what he knows and embraces his ignorance lovingly.