What about Morgannwg?
Glywysing and Morgannwg are not one and the same thing. Only just noticed the anomaly after correcting the infobox and then seeing the heading 'Kingdom of Morgannwg'. That term redirects to here. Their relationship is complicated and the limited sources don't help, but Glywysing and the Kingdom of Morgannwg should have seperate articles. Too late to contemplate doing that tonight though!