I have come across the same thing. The son of a Vicar wasn't registered when born around 1850, but I found his baptism record. I think quite a few births were not registered in those days. On the other hand, I have also come across a woman whose birth was registered twice with several years between. This is because she was given away by her family in 1917 to a couple who had no children ... which was normal procedure in those days as there was no adoption law. The new parents were scared that the birth parents might come back years later when the girl was old enough to work, and to claim her back. For this reason they registered her birth in 1917 to get their own birth certificate, even if the lass was by then 3 years old. Who would ever tell?
Oddly enough, the woman in question married in 1946 ... twice. She had two birth certificates and didn't know which name to marry under, and so the marriage was registered twice on the same day. Nice to be safe isn't it.