Thanks Quaxer for additional information and yes Shane, I need to check all the details but am still a long way yet from making the connections here.
I have a Mary Nobleau (and many variants) married to a William McLoughlin, who seems to be a direct ancestor, having children in the 1780s, 1790s and 1800s, but no family of the same name in Dublin at the time. As the name looked French I took a long shot and checked the Huguenot lists and found Charles Nobileau thirty years earlier. I now need to do much more research.
I've found a number of documents through the internet mentioning this name in connection with the Huguenots but most seem to be on JSTOR for which I don't have a current subscription. I'm just checking at present whether anyone else in my family does.
I can't find a Mary in any of the families on irishgenealogy, and even then it's a big stretch from belonging to a Huguenot family to marrying into a catholic family, so may be totally up the wrong tree, but it gives me a possible direction to check out for further information at a point where the BMD references become very sparse and lacking in detail.
As I see that the Huguenots had their own cemeteries, was it usual for them to be married and have their children baptised in CoI churches?