According to BGG 5 the twins Peredur and Gwrgi were 5 generations later than Coel Hen which would suggest they belonged to gen. 1. However, DSB 12(14) tells us they belonged to gen. 2, see the table below.
|1||Eliffer Gosgorddfawr||Efrddyl||Urien Rheged|
This contradiction can be resolved using HG 12 which states the father of Eliffer Gosgorddfawr was someone known as Letlwm, possibly a corruption of the individual’s actual name, see the table below. He was not Gwrwst Ledlwm who was another son of Ceneu ap Coel. Using BGG 5 and HG 12 the descent of the twins Gwrgi and Peredur from Coel Hen can be reconstructed.
|Gen.||BGG 5||HG 12|
|1||Eliffer Gosgorddfawr||Eliffer Gosgorddfawr|
|-4||Coel Hen||Coel Hen|