The Vatican considers some such ordinations "valid" but "unlawful, or illicit" but the Orthodox Church considers them simply not to be ordinations and thus also considers persons so ordained not to be bishops at all. This is because unlike the Vatican, it considers apostolic succession to exist only in bishops who are regularily ordained by bishops that are neither themselves defrocked, nor teach heretical teachings. Holy Orders are not regarded by the Orthodox as "indelible," thus if an Orthodox bishop breaks from the Church, his episcopacy (and thus his ability to ordain) does not follow him.
Many of these claim succession from the see of Utrecht, or from Orthodox or Eastern Rite Catholic churches; others from Roman Catholic bishops that have ordained their own bishops after disputes with the Vatican. Such lines continue to persist because of the more mechanistic understanding of apostolic succession which the Roman Catholic Church has—that is, if a "valid" bishop ordains a man using the proper rituals, then he is "valid" as well, even if neither has any living connection to the Church. The Orthodox understanding, however, necessarily presupposes the impossibility of episcopi that are vagantes, for the ministry of the episcopacy resides only within the Church.
Many episcopi vagantes will claim their churches variously as Orthodox, Catholic, Apostolic, or any of the other historical names used by the Church. Attempting to trace their roots, delineate one group from another, or easily identify them as being episcopi vagantes can be a difficult matter, especially because such groups seem to be subject to internal schisms and name changes. One indication often pointed out about the webpages of such groups is that they often have a list of their alleged apostolic succession displayed prominently up front and insisting on their "canonicity."
In modern times, some of the major lines of episcopi vagantes trace their succession to A. H. Mathew (deposed from the Old Catholics), J. R. Vilatte (variously Roman Catholic, Old Catholic, and with a line from the Church of India, and Aftimios Ofiesh, a 20th century Syrian bishop appopinted by the Russian Orthodox Synod of Bishops in North America to head the new American Church. The American Church, THEOCACNA, as the SCOBA Orthodox does not recognize these independent ordinations of what would be considered episcopi vagantes. Many attempt to claim their lines come from this Church and bishop Ignatius of blessed memory and we deny this claim.
Many people have claimed ordinations as bishops where it is questionable whether the ordination ever actually took place, which is a separate issue. Further, bishops belonging to groups which are in schism (i.e., out of full communion) from the Church or have suspended concelebrations are not episcopi vagantes inasmuch as their consecrations as bishops were clearly within the Church and the break in communion may well only be temporary. Many (Western, schismatic, especially Anglican-descdent) groups use the traditional/scholastic Roman Catholic distinction between licit and valid orders, tracing a history of ordinations, as a way of claiming legitmacy. The Orthodox church does not generally adopt this distinction. Epsicopal consecration is only valid and licit when in communion with the other Orthodox churches around the world. There has, however, been some flexibilty in understanding in certain cases of schism.