We have placed kits with Y-DNA results into subgroups for distinct families, where two or more kits have results that match each other. In most cases, those results indicate that the direct male-lines for these families have been distinct from each other for thousands of years. For men with Big Y results, FTDNA provides estimates for the birth years of Most Recent Common Ancestors. Those can suggests when the MRCA for men within a group lived, and also when the MRCAs shared with other groups lived.

You can view the FTDNA "discover" tool's "Time Tree" for the Bullock project to see the MRCAs for Big Y kits in the Bullock subgroups:

https://discover.familytreedna.com/groups/bullock/tree

Of particular note: Big Y results for men in Haplogroup R families 01, 01a, and 01b prove their connection to each other and suggest that the MRCA they share was born in about the year 1450. This DISPROVES the theory that the Virginia Bullock line descend from a Bullock man who migrated there from Massachusetts. Instead, the three groups appear to descend from distinct immigrants from England.

None of the other groups appear to have any connections to each other within the "surname era," in the last 1000 years. The results also disprove any "modern" connection between the Bullock families of North Carolina and those of Virginia and Massachusetts. FTDNA estimates that the MRCA shared between the Haplogroup I and Haplogroup R families was born about 45000 years ago.