Sometimes all it takes is a “new” name to open the door to an entire set of memories. My grandmother-in-law remembered a fair amount about her family originally. After a little research, I located the maiden name of her grandmother, which she had not originally remembered.
As soon as I mentioned that last name, more memories came to her mind. Sometimes all it takes it a word or a name to unlock an entire set of memories.
Always go back and re-interview that person when you have located new information.