(Not) Just the Facts
You've selected a type of record, carefully reviewed the indexed content and then set your filters appropriately. But you just cannot find that elusive person. You begin to think they just aren't in the record set.
Are the facts getting in the way? The facts as we perceive them today may not match the information at the time. Maybe there is missing or incorrect information and your filters are hiding the record. Maybe the indexer made a mistake when transcribing the record. Or maybe that elusive person gave an incorrect answer.
Age and date of birth are "facts" that are often inconsistent across the lifetime of those who were born before the age of birth certificates and drivers licenses. It's useful for filtering, but don't depend on it. If you are using a narrow range for a birth year, try increasing the range. It's easier to control the range on Family Search than on Ancestry.
Looking at Mary Maddox Neff, I found that she was very consistent in stating her own age and birth year. Her age was always within a one-year range which can be explained by the date of the census. However, her husband, George M Neff, seems to have taken an anti-aging tonic. He grew two years younger by the end of his life. Their daughter's age was so inconsistent that I'm still not positive whether Elizabeth Ann Neff Shafer had a sister Ann or just changed her name around.
Take a moment to think about that elusive person. Might they have made themselves older to marry, to join the military, to avoid a head tax or to draw a pension? Might they have shaved off some years to avoid the draft, to be younger than a husband or to participate in a program such as Social Security or Medicare?
One of my female ancestors married a man who was ten years younger. Yes indeed, she tried very hard to hide her age!
Do consider opening up the date of birth filter if you're not finding the record you are seeking.