Based on the video explaining the situation. I don't think there is a limit on how many spare rudders each boat is allowed to have, only that all spares must be declared at the beginning of the race. The undeclared rudders do measure in and are otherwise legal.

I can only assume that they didn't exist at the beginning of the race, and that's why they weren't declared.

I expect that the Jury will do what is best for the race as a whole, not necessarily what is fair for this particular set of competitors. After all, only 6 boats entered this edition of the race. The last thing they need to do is piss off Telefonica and end up with only 5 boats next edition.

If I remember right, during the last edition of the race one of the boats had a keel that didn't measure in as legal. The boat was allowed to race anyway, but was assessed a 5 point penalty each leg (or one position further back,) until the keel was replaced with a legal one. So there is a precedent for letting them continue.