We talk a lot about the folly of small segment matches here, which I typically agree with. The one exception that always catches my eye is when I find a new small segment match on a larger segment that I have already identified across other tests.
I found an interesting new match today (through Wikitree) on a shared segment between my uncle (VJ), his first cousin (NB) and their paternal second cousin - 4 X removed (CE). On chromosome 15, we have the following:
VJ and NB - 17.6 cM/3,221 SNPs 65,011,539-79,894,101
VJ and CE - 26.7 cM/5,120 SNPs 65,011,539-87,909,765
NB and CE - 36.8 cM/7,096 SNPs 50,614,631-79,894,101
The only recent shared ancestors between VJ, NB, and CE are A.B. Jones (1836-1902) and Mary Coates (1839-1893).
VJ, NB, and CE each match with Kim (I found her Gedmatch number on her Wikitree profile), on a small part of this shared segment of chromosome 15 between 5.3-5.4 cM:
Kim and VJ - 5.3 cM/1,347 SNPs 69,709,089-77,270,126
Kim and NB- 5.3 cM/1,346 SNPs 69,709,089-77,266,102
Kim and CE- 5.4 cM/1,374 SNPs 69,642,036-77,268,138
Kim's tree is interesting, as her daughter is an active Wikitree user and has her tree well-sourced back to a Van S. Jones, who was born in Kentucky in 1799 and died in Indiana in 1877. In my tree, A.B. Jones had a younger brother who was born in Indiana in 1839, and Mary Coates's mother was born in Kentucky in 1820. Just by looking at our trees, the common ancestor between Kim and my three paternal tests would have to be at least 6-8 generations back.
I was just wondering how people generally react to a situation like this in which a new small segment match appears on Gedmatch for a larger segment that you have already identified in common between other tests.
I asked a similar version of this question on the ISOGG Wiki Facebook group.