Clinog and Clydno have been identified as the same person. The former name is said to be a corruption of the latter. Also, the two names share the same cognomen, which means Edinburgh. However, their pedigrees indicate they were not the same individual as the following table, which uses the manuscript form of their names, illustrates. Clinog was a generation earlier than Clydno.
(Three other sons of Cynwyd Cynwydion who are mentioned in BGG 3 have not been included in the above table .)
In ByS 15 Clydno appears as the father of Euronwy, the wife of Gwaith Hengaer and the mother of St. Gwrwst. In CO his daughter is mentioned in a list of “the gentle, golden-torqued ladies of this Island” as “Eurneid daughter of Clydno Eidin”. The medieval poem Y Gododdin by Aneirin celebrates the valour of his son, Cynon, in the battle of Catraeth which occurred c. 600.
The name Macsen Wledig has been applied to two distinct persons. The first individual appears in gen. -8 of HG 2 as Maxim gulecic, see Why Bartrum’s dating …. I believe this individual can be identified with the Roman emperor Constantius Chlorus as explained in the above link.
The opening lines of The Dream of Macsen Wledig from Pen. 4. (The National Library of Wales)
The Pen. 16 version of The Dream of Maxen Wledig only describes the story up to his stay in Britain. The version in Pen. 4 of the White Book of Rhydderch speaks about his return to Rome, but this continuation is actually referring to the second Macsen.
This is the Western Roman emperor Magnus Maximus born c. 335. He appears in gen. -5 as in the follwing fragment from JC 13.
Cyngar m. Protec
Cyndwr Fendigaid is St. Kentigern who was the son of Owain ap Cyngar and not Owain ab Urien Rheged. The table is in accord with Constantine the Great’s birth in 272 or 273 and the birth of Helena, a wife of Constantius Chlorus, birth between 248 and 250.