One of the key components of the “Reasonably Exhaustive Search” is that “at least two sources of independent information items agreeing directly or indirectly” be used in reaching a conclusion (page 84, Genealogy Standards, Board for Certification of Genealogists (BCG), 2nd edition, 2019, published by Ancestry.com)
Independent information items have unrelated origins (page 79, Genealogy Standards).
While this is a worthy goal, it can be difficult determining that two sources are truly independent of each other in regards to a specific piece of information.
Would a birth certificate and a baptismal record from Illinois in 1890 that contained the names of the father and mother be independent for the names of the parents? After all, they likely had the same informant. Would the parents’ knowledge of their relationship to the child be “unrelated?”
Would a parent-child relationship stated in a family bible’s entry for the birth in 1850 and the statement of that relationship in a 1930-era intestate probate case really be independent? I’m not certain. It would depend or maybe it wouldn’t.
I’m not certain about independence. It’s a gray area that depends upon the black and white–which most things are not.
What I am certain of is that thinking about your sources of information and how that information probably came to be in the record is good for your genealogical research. It is also good to think about how pieces of information from different records in different times and different places may actually have the same origin.