If the time period and location is right, make certain you have accessed the death certificates for all of your ancestors’ siblings. I can think of two female ancestors for whom no death certificate can be located. In fact, I don’t even know when or where they died.
But I do know the names of some of their siblings. In one case the death certificates gave me parental information to work from–although it turned out the siblings were half-siblings and not full ones. In the other case, the death certificate gave a more accurate rendering of the mother’s maiden name.
It’s especially important to keep this in mind if your ancestor died in a state that wasn’t recording vital records when they died. It’s possible their siblings died at a place and time when these items were being recorded.