There are several records on my wife's family in Moline and Rock Island, Illinois, that I've never bothered to get. Part of it is that other records spelled things out fairly clearly, so I didn't see the need to make a trip during the week to the courthouse and did not think some records would tell me anything anyway.
Familysearch released probate records from Rock Island, Illinois. There in a probate from 1907 was a son of the deceased that I really wasn't aware of. His address: the "Feeble Minded School" in Lincoln, Illinois.
It pays to search everything--even those records you've avoided or ignored for whatever reason.