Shocking discovery blows my Irish genealogy

Sometimes, ignorance is bliss. Of course, in genealogy, we don't believe this but I have to say, my shocking discovery has made me wish I had left well enough alone. 

Let me set the stage. In May 1995 I sent to the Commonwealth of Massachusetts for a marriage certificate for Cornelius Donahue and Johanna O'Connor. Did I know that they were married in Massachusetts? No, but they weren't married at St. John in Middletown and their son was baptized there in 1855 so they had to be married somewhere. Cornelius was naturalized in Massachusetts in 1854 so I took a chance sending my request and a check. 

I was rewarded with a certificate that stated that Cornelius Donihue son of Jeffrey Donihue and Johanna Connor daughter of Dennis Conner had been married in Chicopee in December 1853. This was my most spectacular discovery to date. 

In his naturalization certificate, Cornelius told me that he was born in Killarney on or about January 14, 1832,  and had arrived in the United States on July 6, 1847, at age 15. Now I knew his father's name. 

In December 1995 I went to Killarney and looked at the records at the cathedral. I found Cornelius, son of Jeffrey and Johanna Sullivan baptized in April 1833. They were from a townland about 8 miles away. I assumed it could have taken them a while to get into Killarney for the baptism. 

No other Cornelius, born to a Jeffrey was baptized in Killarney on any other date, ever. So for the last 20 odd years, I have been researching this family. Imagine how shocked I was when with the new records available online I was able to search for records relating to any Geoffrey Donoghues and I found a marriage in Killarney in 1878 for Cornelius Donoghue and Bridget Reardon and his parents are Jeffrie Donaghue and Johanna Sullivan. What the what?????

My Cornelius died in 1872 in Portland, Ct from cholera at 40 years old. So obviously, my Cornelius wasn't the son of Geoffrey and Johanna but whose son is he?   I have no clue. The only other Geoffrey in Killarney at this time having children is married to Mary Begley and they don't have a son Cornelius. They also don't seem to have the names that predominate in my family. I have to admit, I always wondered about the whole name thing with Geoffrey and Johanna since their other children also had names we never see in my family. 

So where am I? Back to where I was in 1995 before my trip to Ireland. I so wish the 1841 and 1851 censuses still existed, it would clear up this mystery for me. But they don't and so I have nowhere to go with this.