Today I received a new Ancestry DNA match to a previously contacted and determined by family history research to be a 3rd cousin.
Our shared DNA is 12cM across 3 segments (unweighted 24cM, longest segment 9cM). The Shared cM Project gives us a 7% probability of being 3C.
If it wasn't for our Common Ancestors (which I check for everyday), this match is so low it would have been buried down in my DNA matches and probably never found.
Fortunately I also have access to my brother's results. His match is 105cM across 8 segments (unweighted 105cM, longest segment 35cM). 30% probability of being a 3C.
I obviously missed out on this part of our mother's chromosome.
To add to this I also have my aunt's test results and she shares 175cM, 9 segments (unweighted 175cM, longest segment 38cM). 51% probability of being a 2C1R.
I'm confident with the combination of matches that our paper family history matches our DNA connection.
So if you have the opportunity to test other family members, do it now!
Excuse me now as I go to look at our shared matches to work out how they all fit in our family tree.