Baptism is not compulsory in the UK.
Many people were not baptised, for religious reasons, for financial reasons, because infant mortality was very high. Many people were not baptised until just prior to their wedding, some never. For these reasons, a baptism date is not indicative of a birth date.
A name is, by law, established through common usage, not necessarily by ceremony. It is not even required that you change a name through deed pol, as long as the change is not done to defraud.
When reading original registers, one will also find that at times an incumbent refuses to make entries, because he feels he has not been sufficiently reimbursed.
Another aspect of reading the originals, is that cryptic comments were often added to the margins, giving an unexpected insight into the individual. These are never included in subsequent transcripts.