When you are asking questions of relatives, do you try and learn the origins of nicknames? I have an uncle named "Babe" and for some reason his name popped into my head while walking. It was fifteen minutes before I remembered his real name: Carl William.
What I wish I knew is where his nickname came from. At this point, I'm lucky that the nickname is even known, as I don't think it's used on any legal documents.
Don't forget to ask about those nicknames. There may be a story there.