No not really, but all records are not online, which is maybe why you are not finding them, they also may have been from the UK and took the ferry over to Ireland to take the boat from there or from Liverpool................ at the time of the famine there were many people who claimed to be Irish even though they may not have been as charities were paying their ship passages...it may not be the case for your ancestors but worth looking at UK records...again everything is not online which makes it difficult if you are not UK/Irish based............
During that time the islands of Britain and Ireland were all British people as Ireland was not a separate country , so you see it could easily be done,if they were born in Ireland anywhere on the island then their records will be in Dublin as Dublin was the UK second city and of course also in the church local to where they were born .........................
Add;As I said not all records are online and although family historians are transcribing in Ireland to get lots online they never will all be.....well not in our lifetime. I would suggest you get on some of the specialist UK/Irish forums where you can get specific help by researchers who live here, who are very helpful and unlike some of the huge American forums you are likely to get help within the hour, certainly within days as people will put details of the people you are looking for on their records office list and will even email you the scanned document. I'm English and now live in Ireland and have been transcribing records for near 20 years, so as I say they will not allbe online, the record mountain is high, with over 200 MILES of shelving of records in the National Archive in Kew alone, let alone Dublin Archives and PRONI...we are only just scratching the surface for online... a good site which has lots of UK/Irish links including UK/Irish forums is http://familytimeline.webs.com/apps/links/ look through them all as some are mixed in different sections and they have some transcriptions in the documents page too for both UK and Ireland........you know these ancestors of ours were really inconsiderate, so frustrating!!!
Passenger ship lists in the UK until VERY recently were just boxed, not in order,not indexed and they are just starting to index them now, it would take someone a 3 months full time in Kew just to look through them as you would have to look through them all and travel between mainland UK and Ireland is not documented even now.... I often wonder what someone looking at my life will make of it...sometimes I live in England and fill in the census there, sometime in Ireland and fill in that census...same as voting, working etc good job I write it all in my own 'history'