When I was researching my book, God's Triangle, the story of a scandal involving my Baptist missionary Great Aunt Florence M. "Florrie" Cox, I came across the civil marriage record in Calcutta of her ex-husband and his mistress. The document contained several errors and misleading statements.
Even though the husband, Frank E. Paice, and his mistress, A. Olga Johnston, had been ordained missionaries, they were not above telling a few fibs. Olga gave her age as 32, just a year older than Frank, but three years younger than she really was. She wouldn't have been the first woman to lie about her age, but there was also a whopping deceit about how long she and Frank had been living in Calcutta. Frank claimed to have lived there for seven years, while Olga said she had been there for five years. This was blatantly untrue. They could not have been there for more than a few months as they had been in Australia for at least a year and before that, had been stationed for about six years in remote missionary outposts in East Bengal. Presumably they had lied because of residential requirements for their marriage.
There were several other aspects of the official record that could be seen as misleading, but I won't bore you with those. The point I want to make is that if the civil marriage record had been the first document I had found in my research, I would have been sent down routes that might never had led to me establishing the truth.
Similarly, anyone researching my Australian maternal grandfather, Arthur Joseph George Cox, would have been seriously mis-informed about his life had they gone first to his death certificate. His mistress-then-second-wife, Phyllis, had deliberately not mentioned that he had been married before and fathered 10 children, including my mother, Rena.
Not all errors in official family history documents are deliberate. Sometimes they are just careless mistakes. An example: the death certificate of my Great Aunt and opera singer, Reba Rangan, was wrong in several respects. For starters, Reba was her nickname, not her real name. Then her father was given as "unknown", which wasn't true. Her aunt was named as her mother, which also wasn't true, and it was further stated that she had spent all her life in Australia -- overlooking the fact she lived and worked in London for some time as an opera performer.
The death certificate details had been provided by a nephew and when I challenged him about the inaccuracies, he said simply that he had made no real attempt to establish the facts. He had just guessed most of the information.
I could give other examples of incorrect family history documents, but I hope that I have successfully made my point: treat all certificates with an element of caution.