We honestly never have proven, or could prove it even if we tried to, that fingerprints are 100% unique. It seemed plausible, so people pushed it forward as the truth regardless of reality. Suffice to say, there's a very good reason why police rely far more on other forms of evidence nowadays, though. Kind of tip toeing through a minefield if your case rests on something that might scream "reasonable doubt" in the hands of a skilled lawyer.Noses are basically thumbprints for many animals irl. Ie, no two dogs have the same snoot print!