Jim Bob's date of birth is given as 13th January 1923 in this episode, yet in 'The Runaway' (3x05), it was given as 13th June 1924.
We learn Jim Bob was born on January 13, 1923 with his twin brother Joseph Zebulan, who died at birth.
In the episode "The Secret," there is a frame while Elizabeth is outside (with a basket) talking to Jim Bob about his possible "abandonment on the steps" or having been "left by Gypsies," where she is wearing a red sweater. When she goes into the house to talk to Grandma and her mother, she is not wearing the sweater. Later on, outside, she is wearing it again.
Opening Narration: There comes a time in a young man's life when he begins to wonder how he fits into the world around him. When that time came for my brother Jim Bob it brought the unfolding of a long-kept secret.
Closing Narration: The most valuable truth that all of us learned when that secret was finally revealed is that belonging to a family has less to do with being born than being loved. And with all the hurts and fears and wants we might remember from those Depression years, being loved is what we remember the best.
The German episode title is "Das Geheimnis um Jim-Bob", meaning "The Secret about Jim-Bob".