My grandfather was born in the UK after his father died. His mother failed to register his birth within the 6 months legal time limit. To avoid a fine, she invented a date of birth (26/04/1888) within the limit to register him. This date was about 13 months after his father died, so his 'official' date of birth is at least 4 months after his actual date of birth, which is not known.

Henry Best,
London, UK