In my mind first-hand knowledge would be something that I personally know of. For example information that pertains to myself, my siblings, parents, other family members that I know/knew. To me, second-hand knowledge would be information I got personally from, for example, my grandmother about her parents who I never knew. Is that correct?
Secondly, if I have an original birth/marriage/death certificate of a long dead relation, I expect the source would be the document, and would not be first or second-hand information. Or would it?
One final question. How can a living person state their source as "first-hand knowledge" for someone who lived and died 150 or more years ago?
Thank you for your help... still (always) learning.