In 2010 I participated to the DNA project of Familiekunde Vlaanderen (FV). So I came to know that I and therefore assumed all male relatives, belong to haplogroup U106 and subhaplogroup R-Z18, with the rather rare feature of a micro allel (16.2) on TSR DYS458 (represented as DYS458.2). In 2014 I took part in Family Tree DNA (FTDNA) and got, fortunately, the same result. At FTDNA there are two additional families who originated from Belgium who tested DYS458.2 in U106, but there we expect the relationship before 1280.
December 2016 someone of the Bruges branch had himself tested at FTDNA and a relationship was demonstrated. We should search the common ancestor for sure before 1500, probably around 1450-1475, or at least somewhere between 1320 and 1475. This Bruges branch is of course also DYS458.2 and has a genetic distance of 3 with me (on 37 Y-STR markers). End of April 2017, there were results for another family, unfortunately there was no relationship.
Genetic genealogy has thus already helped and can help further to notice branches as part of our family, even if these cannot be linked yet to our family at this time. If someone (a man) with a variant of the surname De Burchgrave would be R-Z18 with micro allel DYS458.2 we can, except when the genetic details would exclude relationship within 'genealogical' times, consider it proven that it is a member of the same family. A Burchgrave, who would not be R-Z18 does not prove that it would concern another genealogical (legal) family, but that it has a different biological origin. It could also be that the name descended from the same family, but at one time a legal father was not the biological one.
It could help the genealogy of the various branches or families Burggraaf, Burghgrave, Burchgrave etc. if from the different families some men - preferably as distant as possible from eachother in their already described and known genealogy - had their yDNA tested. If men of other families would want to test their yDNA, this can be done via the DNA project Benelux (FV) or with Family Tree DNA.
Peter