Sometimes when you can't find a pre 1855 birth record, for your ancestors it may be because they were baptized in another area.
I had searched for some time for the birth record of one of my xgggrandmothers. I had found her marriage cert, death cert . I knew from the census that she had been born in Scotland. By chance I found that she had been baptized, at 6 years old, along with two brothers in Ireland.