This is like when you're working retail and the scanner glitches or the barcode isn't registered and the customer says "I guess that one's free then!" and you have to say "ha ha, very droll sir" as if you didn't hear that same joke yesterday.
I had a friend named Michael Jackson who went by a different first name. I didn't even know until several years later when he showed a group of us his drivers license and accidentally outed himself.