TIL Type O blood was actually meant to be Type Zero blood, due to lack of glycoproteins in the red blood cells. It was misread as type "O".
I guess you can call it a typo.
Interesting misconception regarding Type O Blood
Initially, the medical community referred to it as 'Type Zero' blood, due to the lack of glycoproteins. The term was misinterpreted to what it is today. You could venture as far as saying it's a **typo.**