Now it is possible that our second example may be Samuel's brother; though equally it may be another James McIlhaggart. James appears as the father of the groom at a marriage in Donegore, County Antrim, Ireland. The strange thing, which makes this entry new to me, is that the groom's name is Richey Kennedy. Samuel's brother James married Jane Harvey and they did have a son Richard in 1832. However, although he was a Merchant Seaman, I have no evidence that he went to Ireland, nor that he married. The Ireland Marriages 1619-1893 record names the bride as Ellener Boyd. It is of course feasible that he met an Irish girl - there was a lot of coming and going between Ayrshire and Ulster - and that the marriage took place in her home townland. There is no known Kennedy link to this family but it is possible that Richard changed his surname, or that he was informally adopted by another James McIlhaggart.
My third example I would like to dismiss as another variant for McIlhagga, and it is that, but it is more. In Scotland Births John was born 25th June 1867 in Middle or New Parish, Greenock, Renfrewshire, to John McIlhaggart and Mary Stewart. I know that John senior was the second son of William McIlhagga and Agnes McCosh. John must have used the name 'McIlhagga' as a boy, but perhaps there was an occasion when he was called McIlhaggart and he made a conscious or indeed an unconscious decision to continue to use it. Certainly the variant occurs for John and for his wife in several instances, for example in the 1881 Census, and most clearly at John's death. McIlhaggart seems to be more a deliberate variant than an accidental one.