My son wishes to apply for Irish citizenship and subsequently, a passport through descent from my Irish born mother. Having checked on online on the dfe site, he is definitely eligible but my mother’s birth was never actually registered so we cannot obtain a birth certificate for her! I’ve wriiten to the HSE and they’ve checked and confirmed that this is the case. However, after my mother married my British father, she applied from UK citizenship and has an official certificate confirming her registration and also her Irish place of birth. She has also had 4 consecutive UK passports, all of which confirm her Irish birth town.
We have a definite paper trail of official documents showing direct descent between the three of us - except the wretched birth certificate. Will this be an insurmountable hurdle on my sons application?
I’ve tried ringing so many departments and embassies and either end up getting referred back to where I started or the dfe website. My son has started to joke that no one actually gets to speak to the Irish embassy and a decision made unless the planets are in perfect alignment!

Many thanks.