And here's the other monkeywrench...

My last name is Davis, and while Welsh, it is listed as a sept of the Scottish Clan Davidson...

I have Scottish Ancestors on my Father's side by way of Urquhart and McIntyre, and Scottish Ancestors on my Mother's side by way of Bruce and McKaye. These ancestors were not Ulster "Scots-Irish" but American transplants in the mid-1700's directly from Scotland. These are not very direct lines (matriarchal on all accounts, all Scots women married into my mostly Welsh and English Patriarchal family)

But I wear the badge/tartan Davidson, and am a member of that clan. Why? Because when I started my journey I assumed my name was a sept of Davidson, so I learned the clan history, motto, etc... joined the society, and feel at home with this particular clan.

I had a bit of an identity crisis when I discovered my surname had no Scottish origin whatsoever, but then realized that my clan was more than welcome to adopt me, and I them... regardless of who my ancestors procreated with.