You are right I misread the article . I took the ‘it’ to refer to Queen Marie’s not Beaugrants.

Hannover Necklace

That means there could be three

Slightly off topic but is there any evidence that the pearls were indeed owned by Marie-Antoinette. It’s odd that the Sutherlands were so open about how they gained them, after all, she did have a daughter and a Brother-in-law. I’ve not heard that they were given as gifts.