ROME — Although nobody much noted it, last month marked the 53rd anniversary of one of the most consequential papal edicts of the past century: the apostolic letter “Ecclesiae Sanctae” ([“Governing] of the Holy Church”), issued by St. Pope Paul VI in June 1966, which, among other things, established a retirement age of 75 for Catholic bishops around the world.

Despite the mythology that Catholicism is a tightly controlled and rigidly centralized monolith, the truth is that the Church is actually one of the most decentralized institutions on earth, leaving the vast majority of decisions about how to apply and enforce Catholic teaching in the hands of its middle managers, meaning diocesan bishops.

As a result, nothing any pope ever does is as critical to shaping culture in the Church as the bishops he appoints.

With a mandatory retirement age, Paul VI ensured that he and future popes would have regular opportunities to shuffle the deck. Popes don’t have to accept a bishop’s resignation at 75, but Paul VI’s decision and subsequent amendments to canon law have ensured that the choice is entirely in the pontiff’s hands.

That episcopal deck may be in for a new shuffle in coming months, as several tone-setting prelates will either hit 75 or continue to sit uncertainly beyond it.

In the U.S., this June alone saw four bishops hit the magic age: Cardinal Sean O’Malley of Boston, Archbishop Robert Carlson of St. Louis, and Bishops Nicholas DiMarzio of Brooklyn and Edward Braxton of Belleville, Illinois.

In O’Malley’s case, at least, the fact that the calendar has turned will likely have little immediate impact, since he’s both the head of the Vatican’s Pontifical Commission for the Protection of Minors and a member of the pope’s council of cardinal advisers.

The commission is helping oversee implementation of Francis’ new rules on clerical abuse, while the council is nearing the finish line on an overhaul of the Roman curia.

Until the pope is satisfied that both of those projects are more or less nailed down, it’s probable O’Malley will remain in the saddle.

The four Americans who just turned 75 join 11 brother U.S. bishops still in office despite being beyond the age limit, a list headed by Cardinal Edwin O’Brien, serving as the grand master of the Equestrian Order of the Holy Sepulchre despite finding himself at the age of 80.

After that, the next-oldest active American prelates are Bishop Richard Pates of Des Moines, Iowa, and Archbishop Gus Di Noia in the Vatican’s Congregation for the Doctrine of the Faith, both of whom are 76.

In September, another notable American prelate will hit 75 and dispatch his resignation letter to Francis: Archbishop Charles Chaput of Philadelphia, who, since his first appointment to Rapid City, South Dakota, in 1988, has loomed as a key point of reference for the Church’s conservative wing.

Apostolic Nuncio Archbishop Christophe Pierre (left) plays a key role in the process of replacing retired bishops in the U.S. Two of the highest ranking Vatican officials, Cardinal Marc Ouellet (center) and Cardinal Luis Ladaria (right) are both over 75. (ALL PHOTOS COURTESY CATHOLIC NEWS SERVICE)

Elsewhere, the situation is similar. In Italy, for instance, the current president of the ultra-powerful Italian bishops’ conference, Cardinal Gualtiero Bassetti of Perugia, is already 77. His predecessor in that job, Cardinal Angelo Bagnasco of Genoa, is 76, and in October, Archbishop Cesare Nosiglia of Turin will also turn 75.

In the Vatican, there are seven heads of departments over 75, meaning their resignations are on Francis’ desk: Cardinal Marc Ouellet at the Congregation for Bishops, Cardinal Luis Ladaria at the Congregation for the Doctrine of the Faith, Cardinal Giuseppe Versaldi at the Congregation for Catholic Education, Cardinal Beniamino Stella at the Congregation for Clergy, Cardinal Leonardo Sandri at the Congregation for Eastern Churches, Cardinal Lorenzo Baldisseri at the Synod of Bishops, and Cardinal Gianfranco Ravasi at the Pontifical Council for Culture.

In addition, the Secretariat for the Economy is vacant as Australian Cardinal George Pell is over 75 and currently in jail awaiting the results of his appeal following a criminal conviction for “historic sexual offenses.”

Collectively, what all this means is that the second half of 2019 could prove to be a turning point in Francis’ efforts to translate his vision for the Church, usually expressed in soundbite fashion as a drive for “pastoral conversion,” into day-to-day reality, both in Rome and in the pastoral trenches around the world.

In the U.S., the man in charge of helping the pope fill bishops’ slots is French Archbishop Christophe Pierre, the nuncio, or papal ambassador. At least in theory, the nuncio is the key figure in making bishops’ appointments, surveying dioceses and proposing what’s known as a “terna,” or a list of three names, to the Vatican’s Congregation for Bishops, which in turn submits its own “terna” to the pope.

In reality, Francis occasionally ignores those “terna” when it comes to the most important spots, as he did in the U.S. in 2014 when he named Blase Cupich as the new Archbishop of Chicago.

In the little over two years he’s been on the job, however, Pierre has carved out a reputation as very much Francis’ man, and in the upcoming American moves, perhaps beginning in Philadelphia, Pierre’s counsel may well prove decisive.

If nothing else, that ought to make Tuesdays at 6 a.m. Eastern Standard Time more interesting this fall, because by tradition American appointments are often announced on Tuesdays, and 6 a.m. (noon in Rome) is when the Vatican news bulletin containing those announcements is released each day.

In other words, Tuesdays in 2019 will be “must-see TV” … so, as the saying goes, stay tuned.