The serial number is meaningless. Your big premium jump will come in the 30 days after the Queens passing. Remember how Michael Jackson stuff spiked hard then crashed. Same thing will happen with anything queen related.
"Certificate of Ownership"?! I'm guessing they don't want to stick their neck out with a guarantee of authenticity.
Well, it is a Royal Mint issue, at least. Most of the coins are from places which primarily issue commissioned "Commemorative" work like Niue, and have appeal only to those who collect non-circulating issues, but I was able to find a few sales records and some currently on offer.