Just a heads up.
Your background might not be/is not your your DNA. So you can't always expect your paper trail to match your DNA. Ie. My mother's parents were both born in Ireland, and traced back in Ireland - many generations. So one would assume she is a very high percentage Irish given her background. She and her family know no other ancestry.
However, she is only 60% Irish - from two Irish born parents, and grandparents, great grandparents etc..... (some backgrounds are very mixed but native Irish are not and tend to average around 98% Irish, whereas Great Britain is more along the lines of averaging 60% for native of that ancestry.).
She carried a good percentage of other areas that would have influenced their travel over centuries. Scandinavian - besides Viking travel - we suspect her Irish father traces back to Norway or Denmark way back. Because of the heritage of his last name.
Also, you can have a situation where you do not grab certain ancestry DNA from one parent, even though they clearly have it. It really is a crapshoot. Google it.
But one sibling can carry what you didn't get through your parents. One tester was sad about her lack of native ancestry that she had been told for generations. She then tested her four siblings. Three had none, like her. One carried 19%. That's how it works. It's very interesting.
Plus, remember there are secret adoptions, affairs and sexual assaults in throughout history - unfortunately. That all affects our findings.
There have been many stories of *surprises*. I read about a man that accused AncestryDNA of erroneous practices.. He picked up a ton of Italian ancestry and knew he had none in his family. Later his elderly mother admitted his father was not his father, that an Italian family friend was his father.
I can't imagine if you find secrets right away. A la your real sibling or mother or father has already, by coincidence, completed the same test. They will come up on your dna match.
_________________________________________________________________
Google LLCoolJ's finds on the PBS show. Secrets no one knew. Including his own mother. Not ancestry per se, but through DNA findings.