Thank you for your polite and well-reasoned reply. I understand that you run a similar service and I'm sure you have a lot of experience in calmly explaining your technology to people. Let me pick up on just a few points.
I chose da Vinci's work because it is out of copyright. There was no verification on Verisign's platform - nor any evaluation of the art. I could easily have used Hirst's name and artwork.
The reason I talk about authenticity is because that's what Verisart were talking about at CogX. I got the impression that they thought stolen and fraudulent artwork was a problem. I'm not an art dealer, so I can't comment on that.
You say that a digital certificate can't be forged. I think we both know that's not true. If a certificate issuer gets hacked, or their credentials get stolen, then fraudulent certificates can be created. We see it all the time with malware. Blockchain reduces some risks, sure, but it doesn't stop human fallibility.
Good luck with your start-up.