It is simply a certificate that says the object you hold is authentic, and not a fake or misrepresented.

The certificate can be issued by anyone who is knowledgeable enough to tell you if the item is real or not. And then the strength of the certificate would depend on who issues it.

I don't know why time is more important than proving it is an authentic coin, straight from Mike and not loaded by someone else. You know what year is on the coin, and you can see in the blockchain when the bitcoins were sent to that address. What else matters?