Hi Louis,
Not quite an expert, just being very observant.
I then made a photocopy of the actual ptg and did the same perspective analysis. And guess what? The original ptg has no single but at least two VP. Which how ever you spin it, this ptg lacks technical rigour!!!. Whooops.... Never mind. Even other great artists {eg Gros) lacked technical rigour. I belong to the cult of conspiracy theorists hahaha.