I have read both threads about these Wedding Gift pieces and understand that they are of particular interest because of the family connection to Paul Ysart and that the story is quite genuine.
Unfortunately, in my experience, there have been many such stories related, particularly with items that have turned up over the years in auctions, particularly in the Perth area. Rarely do they have any documentary proof, such as a hand written letter by the original recipient stating the linkage to the Ysarts. As a result they tend not to attract a premium, rather the value is based on the colour way, shape and aesthetic appeal. This is because when the collector, or dealer, who purchases the piece(s) wishes to resell, the story can only be passed on apocryphally. For true provenance there should be a paper trail - whether this is in note/letter form, or through auction and/or gallery evidence left on the item.
This is especially true in the art market and it is that model that sets the precidence with reference to the original sale through such and such a gallery or auction - directly fro the artst or original collector. This process traces the ownership through to current time and creates the provenance.
Maybe a letter from the current owner stating what she knows with a much information as possible about the history would help the pieces along should they decide to sell them?
However, for me whay Gary has mentioned in the other thread about the vase has validity and is backed up by the evidence that is available about the actual gift given to the Royals.