"Signature" quality diamonds in "Virtual" inventory?

Except for those truly versed in the subtleties of diamond cut, I would expect many new buyers to gravitate towards “Signature” cuts for reassurance. Obviously, cutters/vendors have an extensive understanding of what makes a diamond truly brilliant and they are therefore able to select stones of extremely high caliber for their own “Signature” inventory.

My question is thus: can a diamond of this same high quality really be found in a category other than “Signature”?

I know many people feel that there is a premium attached to “Signature” category stones and high quality diamonds can be found without this branding, but… if a company lists a stone in their inventory, they must have at least taken a quick look at the specs, right? If the stone really was of extremely high quality, why didn’t they select it for their Signature collection?

It therefore follows that any diamond NOT in a Signature collection must not be good enough (rejected for their Signature collection), and therefore the top quality stones can ONLY be found in a “Signature” collection. Or is this just what vendors would like you to believe? If a diamond is truly of the same extreme quality, why would it not have been placed in their “Signature” collection? Do vendors simply not know about all the stones they have in their inventory, virtual inventory included, and therefore top quality stones can be found in a virtual inventory? Or is the consumer’s thinking that you simply can’t tell the difference between a top “virtual” stone and a “Signature” stone, and that there are stones of the same beauty to be found elsewhere, even if they aren’t technically as good as a signature stone?

Consumers: how do you rationalize thinking you can get a top quality stone when it was not selected for a vendor’s “Signature” collection? Does it just have to do with individual priorities (i.e. you don't care about some things that are necessary for a stone to be "Signature")?

Vendors: how do you select your “Signature” stones? Do you agree that every signature stone is better than every other stone in your inventory (all things, inclusions, weight, dimensions, color, etc, besides cut being equal)? Or is it a Signature stone because of a combination of these elements and more than simply a reflection of the cut quality?