[tialaramex]

The site actually has an entire Blog Post about the Duchy of Cornwall https://whoownsengland.org/2017/03/15/what-land-does-the-duc...

Basically the answer is that the Duchy pretends that it is simply a private person (Charles Windsor) and so it shouldn't be subject to any more prying into its affairs than would be the case for you or me. This is sufficiently arguable that it doesn't fear ridicule.