In the May-July 2017 issue of the IFHF’s Newsletter, Barbara Murphy has a wonderful Research Tip.
She recommends John Grenham’s Irish Roots Blog.
A post there is entitled “Why are Irish Records so Weird?” Grenham recently presented the topic for Legacy software’s FamilyTreeWebinars.com library. On his blog, his written discussion is featured. See https://www.johngrenham.com/blog/2017/03/16/why-are-irish-records-so-weird/