Article one traces the mainstream disputes over apostolic succession between recognised church bodies. A separate and stranger phenomenon sits alongside them: individuals and tiny groups holding, or claiming, a technically valid line of episcopal consecration while belonging to no communion that the mainstream bodies article one names would recognise as a church at all.
Scholars and church historians use the term episcopi vagantes, wandering bishops, for this pattern, which grew substantially from the nineteenth century onward as various figures obtained consecration from bishops willing to ordain outside their own church's discipline, then passed it on to successors of their own, sometimes founding jurisdictions of a handful of members each. The result is a considerable number of individuals who can trace a documented, arguably valid chain of hands back to a recognised historic church, exactly the mechanism article one describes as constituting succession, while standing in no relationship of communion or shared teaching with any body whose authority that chain was meant to transmit. The phenomenon is usually cited as evidence that a valid chain of consecration and a functioning church are not the same thing.
A more orderly case of succession crossing communion lines is the Bonn Agreement of 1931, by which the Old Catholic churches of the Union of Utrecht, who separated from Rome after the First Vatican Council's definition of papal infallibility, and the Anglican Communion, whose orders Rome had declared invalid in 1896 as article one notes, formally recognised each other's orders and entered full communion, each accepting that the other possessed genuine apostolic succession despite lacking Rome's approval for either.