Once again many thanks for clarifying those points raised by me. I do understand that baptism and marriage records are recorded by location only as in 'Oylgate' (St Davids RC) or 'Glenbrian (St Peters RC). I forgot to mention the following.
In the late 1970s or early 1980s John Furlong of Burlington, Ontario, Canada, commissioned researcher Ian Cantwell of Dublin, to carry out a research project by recording ALL the known Furlong baptisms, marriages, and deaths, of every parish in County Wexford. I have a copy of this which has proved an invaluable aid to me in my researches; in this the records are recorded by their district or parish name, and not by specific church names. It would appear to me that Ian Cantwell has carried out this project by visitation to Wexford Records Office/Archives where most, if not all parish registers have been deposited. But it is clear that he has visited certain churches where the registers have remained, as in the case of Oylegate. Every parish is listed and so it appears that all early records/registers did survive. However, regarding the missing records for Oylegate previously mentionerd. Ian Cantwell obviously visited Oylegate to record his data, and in this it is noted baptism and marriage records are missing for the period 1820-1830. When I visited Oylegate, and Glenbrian, in 2001 I recorded every Furlong that I came across and was able to construct several Furlong family trees, and I was able to confirm that the 1820-1830 records were missing. .
Once again many thanks for your valuable comments and guidance. I would welcome any further guidance you can offer.