Just because seemingly different sources agree does not mean that they have to be correct–it just means that they agree. Consider whether or not the sources are truly independent. Sometimes different “sources” have the same actual person directly or indirectly providing the information. My grandmother’s 1935 marriage record, 1994 death certificate, and 1994 obituary all provide the same place of birth for her.  Grandma was essentially the informant on all three because her children provided what they were told for the death certificate and the obituary. And all three gave places different from Grandma was actually born. Just because Grandma was consistent does not necessarily mean that she was correct.
Some researchers ask “Why search for someone I already know ‘everything’ on?” or someone “I’m not really researching?” This is why. Because they can lead you to someone else. A search for my great-uncle, Alvin Ufkes, located a reference to him as a pallbearer at the 1962 funeral in Quincy, Illinois, for sister of his grandmother . I may never have located the death notice and the obituary for Anna Buhrmeister (a few days earlier) if I had not searched for my great-uncle in the collection from which this image was taken.  
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