I believe I have established beyond doubt that the M222 SNP Greers from the USA who have submitted to DNA testing are, with one exception, descendants of a member of the family of Grierson of Lag. It follows that any Greer who tested I1 is not a descendant (in the male line) of the Lag family.
I will shortly (probably mid June) be publishing an updated chart on our website, and will advertise it when I do. In it you will see the three separate lines of Greer (Scots, Irish, Viking), and within each group it is possible to see family relationships.
It is an unfortunate fact that some will be disappointed in the outcomes of DNA testing, because beliefs long held in a family can be disproved. In my case, I was taught to believe in the MacGregor genetic relationship with respect to the Griersons. This relationship does not now, and never has existed. Indeed, Grierson is as old a name as MacGregor, which was first recorded at the end of the 14th Century.
I'll post again as soon as the results for the 111 marker testing are in.
David Grierson in Melbourne