Is an authentication opinion a certificate of authenticity?
In short: No. It is a written opinion with the method and photographs. A certificate implies a guarantee that no honest method can give; a documented opinion is something a buyer, seller or insurer can actually check.
Certificates are easy to print and hard to question. That is exactly the problem: a piece of paper that says "authentic" without saying how you know gives the holder nothing to check.
My sheet names every test, shows the photographs and states the limits. If someone disagrees, they can see precisely where and why. That is the difference between proof and a promise.