Tracing a family history can be time-consuming and expensive but worse, the time and expense can lead to incorrect conclusions.
My experience of investigating the families of three John Campbells led initially to assumptions which later proved to be false. But only when additional information contradicting formal birth registrations came to light.
It may be rare but occasionally informants make false declarations when filing a birth or death. In the UK this is classified as perjury and the penalty is a fine or imprisonment so the informant takes a considerable risk if false information is provided.
In my cases the motives were admirable i.e. the protection of a child whose birth was illegitimate. Nevertheless in both cases the informant committed perjury.
The link to this website provides detailed explanations of what information should be provided for each column on a certificate. Look in particular at the section for ‘father’s name ‘ on a birth certificate. From this one can establish the status of the child if the informant has provided the correct information. If on the other hand one is aware that the child is illegitimate but the birth certificate suggests otherwise then one can deduce that the informant has perjured themselves.