If the Grandparent Was Born in Northern Ireland
A grandparent born in Northern Ireland holds an Irish line: section 6 says the island of Ireland, and section 7(2) says their silence does not break yours.
Tag
Civil-Registry
The Foreign Births Register: Registered Before the Child Is Born, or the Next Generation Stops
The Foreign Births Register decides when Irish citizenship begins, not whether you have it: the entry date, the 1986 proviso, and who the timing excludes.
The Irish Line: a Grandparent Born on the Island of Ireland, and the One Rule That Decides the Rest
Irish citizenship by descent from a grandparent born in Ireland: the line reaches you, and one register entry decides whether it reaches your children.
Born Before the Country Existed: 1922, 1920, 1947, 1861 and 1871 as Cut-offs
A citizenship by descent cut-off date can predate the state itself — 1861 Italy, 1871 Germany, 1920 Poland, 1922 Ireland, 1947 Canada. What each one decides.
Registration, Proof, Certificate, Confirmation: What Each Country Calls the Grant, and Who Issues It
Registration, proof, certificate, recognition, confirmation: what a certificate of citizenship by descent is called in each country, and who issues it.