The fingerprint is usually a string create with an hash function that guarantees the correctness of the information. Using the first/last 4 chars does *not* do this, of course, because the inner part could differ; in fact it is possible to brute force-forge a npub with the same 4+4 chars. Because of that, I used the word "fingerprint" in quotes.
So it is only probabilistic, but it is also unlikely that someone would spoof my mom account ;)
Adding a real fingerprint is possible, but we need a trade-off between robustness and ease of use, I don't know if it is worth it.