As is well explained in Evidence Explained by Elizabeth Shown Mills, when we examine a document for genealogy evidence, we consider the informant, and how reliable they likely are for the information given in the document.
My own birth registration illustrates how even usually reliable documents can fail us.
The informant for my birth registration was my mother. One would think she would be a reliable source for her own birthplace. Unfortunately, she indicated she was born in Vancouver, BC, Canada when in fact she was born in St. Catharines, Ontario, Canada.
Her own birth record, which I had to copy and send to correct my birth registration when I was an adult, indicates her birthplace as St. Catharines, Ontario, Canada. She always told me she was born in St. Catharines, and my birth record is the only document (that I know of) where she stated she was born in Vancouver.
So my own birth record demonstrates how even ideal informants can give erroneous information. Had I not had my identification stolen, I may never have seen the actual birth registration and corrected it, and some future genealogist would have had quite a hard time finding my mothers birth record in Vancouver, which is very far indeed from her actual place of birth!
My birth record also contained some other quite possibly erroneous information which I will discuss further on the entry for my father.