That's right Jock. My Duncan's were from Fife and although Perthshire is not far away I'm not sure that they took the name from Donnchadh the Stout. The first Earls of Fife were named Donnchahd too. All depends how far back the family goes in an area. In saying this I guess the idea of clan is like-minded people that band together. Historically not all clanfolk were related and allegiance sometimes changed. So if you find a clan that you feel a connection with go with it. We see this at clan tents alot. Some names are commonly listed as septs for multiple clans. Folks will ask which clan they should be with. I'll ask where was your family from and if they don't know I just tell them find the clan having the most fun.