Thank you all for the amazing info - I think I'm really starting to get a feel for the kind of life Michael McChrystal and his family would have been like.
Maiden Stone: The only birth I've seen that would fall under the civil registry is the previously linked one for Thomas Edmund in 1865 (I believe he may have been the youngest child of the family). The informant was a woman called Sarah Morgan, who I believe is likely the same woman shown in this
1879 death record, so you may well be right about Michael being away from home at the time.
It seems to me that the family movements seem to revolve around land - specifically the farm in Annagh. Michael's father (also Michael - all the eldest sons in this family seem to be named Michael) dies in 1875. As his eldest son Michael and his wife Susannah are seemingly still over in England at this time, he wills his interest to his daughter Mary who holds it until Michael returns and takes over. Michael's sons all marry in Ireland but only the eldest (named Michael, what else!) remains in Ireland. His other brothers return to England and seem to adopt their father's travelling manner of work until they finally settled in North West England.
I'd assume it's a case of the small farm only being able to support the one family, so one holds it while the others go and hit the roads for work. Maybe that's what initially brought Michael (the initial subject of this thread) to go working on the railroads.