Ulster naming pattern was as you describe and some families certainly seemed to follow it at least until the last few generations but other families didn't so it really can't be used to guess at names of grandparents, etc.
Another Ulster custom, especially comon amongst Presbyterian families, is to name children after minister, doctor, schoolteacher, landlord, etc. Also, surnames (family ones and otherwise) often used as middle or even first names for boys and girls.
As far as 'lost' Irish records- the biggest problem is census records. No civil registrations (birth, marriages, deaths) were destroyed. Many Church of Ireland registers sent to Dublin for safekeeping were destroyed but surviving Presbyterian registers are almost always in local custody/available in PRONI, etc.