When the English first arrived, the whole island was Gwales and spoke Gwalisc (Gaulish). With no border patrols, there were no borders.
As the use of English spread, the English-speaking areas became Englaland. But Welsh hung on for centuries in separate western areas - Cornwall, central Wales, and Cumbria/Stratchclyde.
And the old stories were retold and elaborated in the areas where the old language was still spoken. Some of the Old Welsh literature comes from the north. Y Gododdin is set in southern Scotland.
And obviously the Old Welsh-speakers in Carlisle (a Welsh name) had no reason to regard Cardiff as the centre of their universe. The modern attitude that tries to claim everything Old Welsh for modern Wales is quite misleading. (Though oddly we don't seem to see the Scots trying to claim any of it as "Pictish", though they could)
But the bards in each area would tend to set the stories in their own area. In Cornwall, it was all about Cornwall, in Wales the same stories could be set in Wales, and in the north, they were tales of the north.
Which makes no sense where Arthur is concerned. A Brtish warlord holding off the early stages of a Saxon invasion is fighting in the east. If he's in the west, England is already conquered.
Camalot is the Old Welsh name of Colchester. Nothing says Arthur's capital was at Colchester. But it wouldn't be silly.
