If you've never heard of a place called Hen Ogledd, Wikipedia can give you a good start. After the Romans left Britain in the early 400's, Angle and Saxon invaders drove native Britons westward into Wales -- and northward into Hen Ogledd, the "Old North", located, in today's geography, in parts of England's north and Scotland's south. By 700, Hen Ogledd had been conquered by Picts coming south and Angles moving north, and the Welsh-speaking Britons who were not absorbed by their conquerers fled to Gwynedd or Powys in Wales.
WikiTree has some profiles for persons who lived in the Old North. Whether they can be well documented or forever live in "Uncertain Existence", their places need to be identified.
Other genealogy sites might say they were in England, Scotland or Wales, but Wikitree prefers to identify places closer to what the person profiled might have used. Compounding this is that they spoke a Welsh-like language and ended up in Wales, but while in Hen Ogledd were geographically in England, Scotland, or both.
I propose the following:
1. In the data field for place of birth, marriage or death, enter the applicable Kingdom if known, then Hen Ogledd, then Britain.
2. Categorize them in a geographic category Hen Ogledd which could be a subcategory of all three -- England, Scotland and Wales.
3. Project oversight would be Medieval or Wales, since the names follow Welsh patronymic rules and are really part of Welsh history (although the peoples who defeated them are part of English or Scottish history).
We're not dealing with a lot of names here, and some will never be well documented, but they exist on WikiTree and a consensus on how to place them would be helpful!