There is an additional set of genealogies which contain an "Arthur" of about the right time (Kirby* suggests c.575 CE) : those from Dyfed. There are four versions, of which the most important are that found with in an undated but early Irish story "The Expulsion of the Déisi"* (Translation Version 1; Version 2):

Tualador (most recent) - Rigin - Catacuind - Caittien - Clotenn - Naee - Arthur - Retheoir - Congair - Gartbuir (Vortepor) - Alchoil - Trestin - Aed Brosc - Corath - Echach almuir - Arttchuirp (oldest)

and that in the Harleian MS. 3859* (our Manuscript A):

Elen (most recent) - Ioumarc - Himeyt - Tancoyslt - Ouein - Margetuit - Teudas - Regin - Catocaun - Cathen - Cloten- Nougoy - Arthur - Petr - Cincar - Guortepir (Vortepor) - Aircol - Triphun - Clotri - Gloitguin - Nimet - Dimet - Maxim guletic - Protec - Protector - Ebiud- Eliud - Stater - Pincr - Misser - Constans - Constantine the Great - Constantine (oldest)

However, the general confusion of the genealogies, the fact that they don't fit with any other tradition, and the obviously spurious nature of some of the names, renders this appearance difficult to comment on.