It was a requirement to register full details of a child’s birth within 21 days. Failure to do so invoked a fine and in rural areas particularly, the 21 day deadline for registering births was frequently disregarded. In order to avoid payment of the fine the dates of birth were adjusted to comply with the deadline. Where Church records give the dates of birth these are generally more accurate than those given in civil records; however, variations of up to nine months can occur. Please contact the county genealogy centre from which the record came if you have a query about a particular record.
above compliments of an excellent search site
This may help in part to explain why a child was "BAPTISED BEFORE HE/SHE WAS REGISTERED AS BEING BORN" an impossible task in logic !.
There may also be a connection (legal requirements) why the age discrepancy in the 1901 and 1911 Census of Ireland was quite common.
I have found that in general the 1911 details were more accurate.
Information regarding births, marriages, and deaths was not always recorded and, even when it was, it was not always written down accurately, especially in birth and death records. Approximately 15 per cent of births were not registered, especially in the earlier period.
Some people remained unregistered due to the failure of their parents to register them at birth and others who nominally complied with the law made incorrect entries. Much of the work necessary to ensure more complete coverage was completed during the period 1879-1900 when Thomas Grimshaw was Registrar General. The Births and Deaths Registration Act ( Ireland ) 1880 set out the procedures to be followed and the persons who were required to give information to the registrars in respect of births and deaths. It laid down time limits for persons to comply with the regulations and provided a system for the correction of errors. Provision was also made for the appointment of assistants to registrars and superintendent registrars and penalties designed to protect the integrity of the records form fraud were introduced.