Re: The one use
Fails due to need to change the data:
People do change their name. E.g. trans people will want their certificate re-issuing with their new name after they transition. Also witness protection. Also, grades get appealed, degrees get revoked due to discovered fraud/cheating, etc.
Actually, many of those cases should be auditable. For instance, with my degree certificate was information on what to do if your Cert is lost/destroyed. They will issue a new one, but it will have "Copy" marked on it. You only get one "original" and that's it.
If your degree is revoked due to cheating, that's actually useful information in the blockchain - not only can it be seen that you were issued a degree, but also the disgrace that follows (probably breaches GDPR Right to be Forgotten, but from a basic position of academic integrity, it's a matter of historical record. X happened, then Y happened. Though people might prefer to pretend that X didn't happen given Y).
Likewise, changing your name - you get paperwork for that. In the majority of cases it should be an audit-able change for fraud prevention. You don't change your certificate. If you get married, you don't get your Birth Certificate reissued - you have your original records, then your marriage certificates and your change-of-name. In a basic case, blockchain is ideal for recording those immutable historical facts - you were born on day x1 with name y and gender g, you did graduate on day x2 with name y and degree z, and you got married on day x3 and changed your name to y2, you changed your gender and your name on day x4, etc.
It runs out however when you need to subvert the normal order of things for legitimate purposes that need to escape auditing - like building a legend for witness protection, or a spook going undercover. You can't simply insert records because they'll appear in the wrong place in the blockchain - a degree awarded from 20 years ago but only logged last week...