“The succession is uninterrupted, but with the death of St. John, circa AD 100, the faith the Holy Apostles received directly form Christ had to be explained and propagated through the episcopacy.”
Makes sense. Thanks for the response!
It is, of course, just a marker. These were two distinct epoches, but the transition was gradual, as the living Apostles received martyrdom or, as the case was with St. John, were exiled, and the bishops they consecrated did more and more apostolic work.