You appear to be saying that there are people who dispute the existence of the words of the legislation setting up the referendum

Why would I dispute something so easily verifiable?
It is disputed that THIS referendum was advisory because it was pledged that the "advice," i.e. the result, would be accepted whatever it was and without Parliament having a say.

The court case has nothing whatsoever with that,

Of course it has!

it is purely about whether, under currently existing legislation, it has the ability to do that without the approval of Parliament.

That was the pledge given for this referendum, that the advice would be taken and Parliament would have no say about it.
There was no objection to that until the result came in.