I find history fascinating. What I don't find in history is certainty. Unlike many who study history (or anthropology or archeology), I see it quite simply as interpretation. Even written history is often only that which was recorded by the dominant culture and how they perceived what they were observing (since the records of those who were subjugated were often destroyed); this is easily realized when we consider how Europeans misinterpreted so much about Native American culture. If those confusions arose only several hundred years ago, all of it "documented," then it is quite easy to see how confusing history can be going back even further in time.
As I research Celtic history, I find repeatedly that each person is determined to make their interpretation one of fact. During the past years, it seems, there has been a lot of uproar regarding the identification of whether one is genetically "Celtic," but we can no more isolate our genes and DNA than we can our veins and heart. There is even dispute on whether Celtic societies were actually established in Ireland, Wales, Brittany, and Scotland, primarily because of modern linguistics; again, we can only see through a glass darkly on this or any other historical so-called definitive interpretation. I enjoy the research; I appreciate the tremendous effort involved. However, I see the endeavors as portals into what might have been, not what was (as fact), and in this undertaking to find out more about ourselves.
For me, the Celtic legacy remains its culture as a whole, not its parts as isolated components to substantiate whether someone is right or wrong. The whole view, individually interpreted, is what has the potential for helping humanity achieve greater good for every being. In other words, what in this legacy can help us lead better, more balanced lives?
That is the angle I come from, whether in my personal genealogical and family tree research, or in the fictional history of the characters in my novels. In other words, how might Celtic culture have shaped the people of the past? What might I learn from the bits gathered together into various patterns?