Some general points about early parish registers
Parish registers were started in 1538, but the original registers were simply on paper and have rarely survived. However in 1598 it was ordered that registers should be kept on parchment, and that the earlier registers should be copied onto parchment, although for many parishes the earliest surviving registers date from 1598. During the Civil War and Commonwealth parish registers were supposed to become civil registers, and only returned to being parish registers after the accession of Charles II in 1660. This means that there are often gaps, particularly between 1643 and 1660, and for some parishes the earlier registers were lost. There are also cases where individual register volumes have gone missing, while some ministers were quite clearly less conscientious than others in keeping the books up to date
It should also be realised that the registers recorded baptisms, marriages and burials, and that information on birthdays and death days is very rarely available from any source. The early baptism registers often only give the name of the child and father, while the early burial registers often just record the name- with no indication of age, etc. In addition baptisms represent children baptised in the parish church, and as the number of non-conformists increased the percentage of children whose baptisms were recorded in the registers decreases.
As a result of these factors research before about 1660 can be particularly difficult, as one's ancestors may not be recorded in the surviving registers, or the entries are such that one ends up with a spurious genealogy because of ambiguities and inconsistencies in the surviving records. In some cases other records, such as bishop's transcripts, manorial court records, etc., can be of use, but these are rarely transcribed, even less likely to be computer indexed, and are usually in handwriting which can be difficult for the amateur.