Primary information is typically defined as information that was provided by someone who had first hand knowledge of the information. Secondary information is typically everything else. I can provide primary information about my date and place of marriage and secondary information about my date and place of birth as my knowledge of the marriage is because I was an adult when it happened and hopefully was aware that it was taking place.
My knowledge of my birth is because I've read it somewhere and have been told it.
Just because information is primary does not mean it is correct--I could have my anniversary wrong. And just because information is secondary does not mean it is wrong.
The correctness of information has more to do than whether it is primary or secondary.