It seems this is a recent phenomenon. So far, I have not been able to find corroboration for these ordinals in any resource that predates Wikipedia.
: Not just Wikipedia.
: Some other sites do number the Esterházys:
: --Previous Message--
: Wikipedia's article on the Esterházy family
: gives the princes ordinals. For instance,
: the late Fürst is referred to as Paul V, his
: predecessor is called Nikolaus IV, and his
: successor Anton II. I cannot find another
: genealogy that assigns ordinals to the
: princes of this family. Is this an example
: of a Wikipedia contributor taking editorial
: liberties by applying a convention where it
: never existed?