A couple more items I wanted to point out.
The Willie R. Henderson who was born in May 1921 and died in 1948 is not the correct person for this family. Note that his death certificate gives other parents and locations.
According to the 1930 census, your Willie was 7 years old. I found a birth index entry for him. He was born 23 June 1922 in Estill County. His mother's name was Callie Stamper -- not Rallins.
According to the SSDI and KY Death Index, your Willie R. Henderson died 7 January 1993 in Madison County, KY.
Looking again at the 1930 census, Callie is "step-daughter" to William Rowland. In fact, the record says "wife's daughter."
I could not find a birth record for a Nora B in 1918, but I did find one for a John W. Henderson, born 20 November 1918 in Scott County, mother "Allie" Stamper. The age is an exact match with the 1920 census. I think this is the same child.
Your John W. Henderson (Nora) died 3 March 1994, possibly in White County, Tennessee.
Getting obits for the two sons might ensure that you have all the correct info, and might even provide some insight into their history.
I realize that this does not answer the question of when Ben Henderson died, but I wanted to make sure you had all the facts on this family accurately. You never know when info on some other family member will help you solve a problem.