Thanks, that makes sense. That is the only place to search for Agnes' birth in 1892?
Heather
No. Pre 1922 certificates are on irishgenealogy as well as GRONI. But since irishgenealogy is free and you have to pay for GRONI I would generally use irishgenealogy for an 1892 birth.
As has been mentioned earlier, some births were registered without a forename so search with “unknown” as the forename or leave the box blank. Also Agnes is a variant of Ann & Nancy so try those too.
One thing GRONI is very good for is finding siblings. Searching their indexes is free. If you know both parents surnames, enter them on the births search facility and leave the child's forename blank. You can only do 5 years at a time but it should throw up all their children (which you then look up on irishgenealogy).