"Authentic" and "authenticated" are two parallel concepts that are not necessarily the same thing. An authentic item is always authentic whether or not it has been authenticated.
Agreed, but for something to be used as evidence of guilt, I will have to be authenticated.
A related issue is the inevitable appearance That Guy who invariably demands to apply a highly personal standard for authentication.
There is no such thing as demanding a "highly personal standard". A piece of evidence can either be authenticated or it can not.
Said highly personal standard is almost always specifically designed to set the bar impractically high, and rarely resembles what is actually done in practice.
And who decides what is actually done in practice? The person who sets the bar low?
The purpose of all this is to allow That Guy to simply ignore hostile evidence by trying to use a bogus authentication standard to unilaterally declare that the hostile evidence is "unauthenticated," then equating "unauthenticated" with "invalid"
and then there is a guy who uses his low standard to declare evidence valid..... So, where does that leave us?
MW: Agreed, but for something to be used as evidence of guilt, I will have to be authenticated. It's always about you, isn't it?

. OK, just kidding. Mostly.
You will have it authenticated. And, you will of course apply your own personal standard as to what constitutes properly authenticated. And this standard will be designed from the outset to prevent it from being, in your mind, authenticated. But it's all simply nothing more than a ruse to avoid dealing with evidence that you find inconvenient.
MW: There is no such thing as demanding a "highly personal standard"This is exactly what you've been doing.
MW: A piece of evidence can either be authenticated or it can not. Authentication is a proxy for authenticity. It does not in and of itself actually prove or disprove authenticity, especially the latter. Doubly especially when the authentication method is designed from the outset to prevent an item from being authenticated in the first place.
MW: And who decides what is actually done in practice? The person who sets the bar lowThe people who actually do it in practice. In 1963, it was done the way that WC did it: by asking the official who first took possession of the item if he could positively identify it as the thing he took possession of. This process is actually dialectic: what is the evidence that the item is authentic, vs what is the evidence that the item is invalid. There is already evidence that the pistol is authentic, and none that shows that it is invalid.
MW: and then there is a guy who uses his low standard to declare evidence valid..... So, where does that leave us?If I use the unreasonably high standard, I have an item that is not authenticated, but has not been shown to be invalid. If I use the low standard, I have an item that has been authenticated, but has not been shown to be invalid. Either way, it has not been shown to be invalid.