I think that I will have to park this issue for now, but before I do, I note that the irishgenealogy.ie website states that the Killorglin parish, which includes Cromane Upper, says that it has birth records from 1798 to 1911.
But there is definitely a gap in the 1850s, which may simply be because no records were kept. Some births for Killorglin people can be found in both Killarney and Glenbeigh, which suggests that perhaps the physical state of the church was low. Also, we should not forget that the 1840s were the Hungry Forties, and the morale of the entire country would have been at a low ebb, and keeping records low on the list of priorities for both Church and people. The lassitude lasted a generation.
The parish priest from 1884 to 1916, Fr. Thomas Lawlor, was a very energetic man, and it seems that he may have been sent to Killorglin to prevent the parish going under completely. The man built six National (primary / elementary) schools in the parish within three years of taking over, and went on to tour the USA seeking funds for a new church in Killorglin, which was completed (if not wholly paid for) in the late 1880s.
He also rebuilt the Church at Cromane in 1912/13 before his death in 1916. he is buried under the altar in the Lady Chapel in St. James Church, Killorglin.