y-DNA has proved that testees (is that a word?) with the above surnames (plus a few other surnames)are all carrying the yDNA of Irvin of Bonshaw, a puzzle some of us are trying to unravel. There are several exact matches to the Irvin of Bonshaw 67 markers, and numerous 66/67 marker matches. Of those actively trying to figure out when and where the NPE event(s) took place, our ancestors came to Ulster from the area of Liddesdale in Roxburghshire, Scotland. The Irwin (and variants), Armstrong, Elliot and Park families were all Border Revier families with frequent intermarriage amongst them and with other Reiver clans such as Scot, Weir and Bell. Several of the surnames involved appear on the surname map for the Plantation of Ulster, and it is documented that they opted for Ulster rather than face further prosecution in the Scottish borders.
It seems to us that while "indiscretions" might account for one or two of the surnames carrying the Irwin (and variants) DNA, there may possibly have been some sort of major catastrophe (famine, disease, etc.) which might have caused orphaned Irvin sons to have been informally adopted into the clans of Armstrong, Elliot, Park, etc. We've even fantasized that this NPE might have occured after Carlangrig, when Johnny Armstrong and 37-50 of his riders (among whom were almost certainly at least Irwins and Elliots) were captured and hung.
I would be very interested in corresponding with anyone well-versed in the history of the Border Reivers or anyone carrying the Park, Parke, or Parks surname from Ulster.