I see that not all the 13 historic Welsh Counties have been included. This is probably because their flags are not on Wikitree, for some reason or another. I have checked a couple, Denbighshire and Radnorshire and can find no flags.
With reference to "modern" counties like Clwyd, I can find no evidence to show they ever had a flag (please prove me wrong!). They may have had coats of arms, but not, it would appear, flags.
What can I do to help?