It pays to study your family information once in a while.
I was just looking at John and Jennie Smith's family timeline and noticed this small mistake:
1902 - John's father John P. Smith died
1904 - John died
1910 Census - Jennie was widowed, living in Kentucky with her son Jack, widowed sister-in-law Alice, niece Katherine... and John's father, John P. Smith, age 86, who was apparently not dead. Oops!
I later found him in the Kentucky Death Index - he died at age 95 in 1918.