Smith DNA Project Community Forums

Your question is a very good one. Wrote about this subject last year "Thoughts on YDNA versus Autosomal and NPE" 

When you look at the YDNA results, you'll notice that you can find matches, say, on 111 markers, but others may not have done 111 markers, but rather, say, 37. It might be that YOUR Smith line has not yet tested or there are not enough of other people with different lines to zero down into a particular surname. The methodology is to divide and conquer.For example, pick a point in the past where there are additional children to compare with. Without being too specific, suppose you have a Richard Smith from a particular location. Look to see who the children are, follow the lines down and see if you can find a male Smith that is a direct line to that Smith but preferably through another son, if one exists. Does that one match you or does he match Smith (or perhaps a third option). If that one matches Smith but not you, then you know that the variance to a different surname took place after that point in time.

Another action to take it to check locations. That depends on the people you match with having a tree where you can compare; if they do not, you need to write them and ask them for it. What you are looking for there is, is there a location in common at some point in the past. When people travel from one location to another (mililtary, business, etc) that is not a foolproof way to find a match, but it should not be ruled out.