The Old Cumnock Group is designated as such on the basis of a single kit whose whose lineage data gives an oldest ancestor as James Cowan who lived in Old Cumnock and either relocated to Connecticut in the US or his descendants did. Five of eight kits tested at the 12 marker level, including the kit traceing descent from James. Most YDNA matches are found with the 12 marker kits, making these findings of limited use. Kits testing at higher levels show distant relation to most other kits in the group. A recent test at 111 markers showed a moderately close (4.2% dissimilarity) with the kit traceing to James Cowan, but given that the later kit tested at 12 markers, and only 12 markers could be compared, these results are considered unreliable.
Overall, it is likely that the this is an artifiscial group whose similarity with each other is driven by the low number of markers tested by most of the kits. It is likely that most of these kits would show no similarity to each other if the number of markers tested were increased.