I've had great success on irishgenealogy.ie and was interested in your post and the various replies. DISCLAIMER: My views of the site and my degree of success in finding reliable data may not reflect the views or success of anyone else. (Whew. Now that is over...)
I'm not familiar with the family names you identified, by my general obsersations may be of use.
- Records, particularly RC records are of baptisms, not births. The baptism was postponed for any reason, the dates could easily be "off". In the parishes I'd researched, the priest often went to the home and perfomred the baptism there within a few days of the birth.
- The quality of the original document may be poor, resulting in errors in the transcription.
- Images of the original page are a available for SOME parishes and records. I'd not found them for my "parish of interest" in Kerry (Listowell). Perhaps they will be added at some point.
- Whenever they ARE available, always download a copy of the original document. There may be additional information not in the transcript or parish form, such as the names of the marriage witnesses and the fact that they were parents to the bride and groom. Contrary to an earlier reply, I've found these generallly readable.
- Echoing the comment on common name variations, there can also be name differences due to the recording of information. Surname spelling until the past 150 years or so was somewhat arbitrary (in the U.S.).
- Also recognise the commonality of names and be cautious in accepting a find as individual you are seeking. Names we feel are unusual may have been very common for that period, and you may find several records of distinct individuals with the same names.