I am pouring through the family trees of my DNA matches on both GEDMatch.com and Ancestry.com and, while it hasn't helped me solve any road blocks yet in the 2 years since I tested myself, I have noticed groupings of families and even specific names that come up often. What is the likelihood that heavy occurrence of specific names or families indicates an ancestor that I'm unaware of, versus just being a coincidence caused by other factors?
For example, on my Mom's side, we haven't been able to determine what Sherman family her third grandfather descended from. There are not a lot of results for Sherman among her DNA matches, however, the Brownell family of Rhode Island does come up a lot and I know the Brownells and Shermans were close in colonial Rhode Island, USA. Could the fact that dozens of DNA cousins have Brownell family members from colonial Rhode Island in their family tree indicate that my mother's brickwall ancestor is from that family?
Another example, my father's great grandfather was adopted and nothing comes up in his DNA cousin family trees for the biological name, Latour, however, the name Jean Louis Larmeu has come up as an ancestor among his DNA matches dozens of times. Could this indicate an ancestor or could it just be a coincidence that I happen to be related to a lot of people that are related to this person?
Edit: My question is specific to a genealogical principle rather than my particular ancestor and circumstance to engage answers on this principle in general, however, in the example scenarios I provided, the DNA matches do not otherwise have any matching surnames or ancestors and they are all about 4-6th cousins, matching up to the position of my brickwall ancestors, who are my 3rd great grandparents.