There are many names in the Register that are linked to a District Tartans and not a Clan Tartan. Not all Scots were affiliated with a clan historically. I suppose that it is even possible that most were not. There also appear to be many families that have registered tartans for their name that are (or were) already linked to a Clan. But the whole linking of names to one (or in many case more than one) clan seems to be viewed by many with a healthy dose of historical skepticism anyway. As many with more knowledge that I have noted many times, the whole idea of a tartan for a clan is a relatively "modern" notion and one based more on fashion than historical fact.