Who was Nancy Betty?

I have written more than a dozen times about the name McElhago, one of the oldest clan families we have, and some of the names can be found in FamilySearch including John married to Jean Glen, James to Jane Harvey, John White to Christina Fowler, Samuel to Janet White and some offspring, Archibald, John White and Adam White. All these belong to the Scottish family with which we are familiar (see for example my blogs of 5 Feb 09, 20 Mar 09, 5 Apr 09, 23 Apr 09, 16 Jun 09, 16 Dec 09, 8 Jan 10 and 28 Mar 10). There was however one birth from Ireland Births and Baptisms, 1620-1811, where the mother's name was given as Nancy McElhago. This was the birth of William John Brownlees on 17th August 1866 at 0013, Randalstown, Antrim. The father was Alexander Brownlees. I first looked for a Agnes McElhago as Nancy is the familiar name for Agnes, but couldn't find one. Then I realised I have on record the marriage on 27th October 1865 of Alexander Brownlees to Nancy Betty McIlhagga at Antrim Civil Registrar's Office, which is clearly the same couple. However, my problem is that whether the surname is spelled McElhago or McIlhagga I have no family tree in which they fit. The marriage record tells me that Nancy's father was a William, but the only William-Nancy father and daughter known to me is William of Ballycloughan whose daughter Nancy married William John McLeery in 1863, so despite her year of birth having to have been very much the same as that of Nancy Betty (early 1840s), they are clearly different people. I am left with an unsolved problem.

Alphabetically McElhagow follows McElhago, but not historically. Both names are from Ayrshire, but if McElhago spans the 18th and 19th Centuries, McElhagow takes us back to the 17th Century, the earliest reference being to John son of David McElhagow born 26th August 1666 in Kirkmichael, at least on the earliest record from the FamilySearch site. In fact if you have seen my earlier blogs you will know that David, who married Katherin Baird in 1655, was born about 1638 and that he in turn was the son of Thomas McIlhagow born about 1610.