I know they didn't always get it right first time on registering births! My g.grandfathers certificate (registered 1877) originally gave his birth date as 10th Feb.
However, a correction note was added (in1891) giving birth date as 10th January "on production of a statutory declaration" made by both parents.
No idea how/why the mix up happened as it was registered by his mother on 15th Feb 1877.
Anthea