I purchased this set at my local club's show yesterday. It is a set of six gold half sovereign coins containing a 1980 and the 1982 through 1986 coins. This set has all of the trappings of a Royal Mint product. It comes in box marked with the Royal Mint seal, and a certificate of authenticity that looks official. Yet I can't find it listed in the Spink Coins of England and the United Kingdom decimal coin catalog. Does anyone have any information about this set? It seems odd that a government mint would be issuing a set, presumedly in 1986, with prior year coins in it.
I have no way of knowing this for certain, but I suspect it may be similar to what has been done with Maundy Money sets for, oh I dunno, 180 years or so. In Great Britain, and I think there's an actual law that allows it but it may just be a long lived custom, the banks are allowed to assemble, manufacture cases and such, and then sell sets like this to the public. With Maundy Money, cases like these containing the coins are manufactured and the sets sold by the banks - The coins are completely genuine, coming from actual Maundy Sets issued by the Crown - but in bags, not cases. The banks then purchase the coins from those who received them, put them in the bank's cases, and then sell them to whomever wants them. So I suspect what you have may be something similar.
I'd also add John that I collected Maundy Sets like those I pictured above for quite some time. It was kind of theme of mine that carried over from my days as a collector of US coins. With US coins I had a collection of all the Mint Sets and Proof Sets in original packaging. So I looked for and purchased sets in original packaging from other countries when I could find them - after I switched over to collecting world coins. And those of Great Britain were among the easier to find, though none were actually easy. Sets like this, an original mint set issued by the Royal Mint and not the banks. A 1911 Proof set in its original case. Sets like this you will find listed in books like Spinks and the Krause Catalogs. This one in particular, if memory serves, there were 3 versions, each holding a variation of the number of coins. Some sets were even larger like this 1831 Proof Set.
The Royal Mint produce quite a lot of different sets such as this in quite low numbers especially for proof coins and they are legit. I guess Spink doesn't list all of them because they are not single year sets but more a collection of coins put in a box, if that makes sense. I think the Royal Mint do this to make a bit of money to subsidise its visitor centre and museum as while owned by the Treasury i.e. the government, I think it is expected to at least break even on its operations.
You are probably right. The serial number on the COA only has three digits. The set is still only worth its melt value or so.
All I could find is a listing for the same type of set from when Apmex had one for sale on their website. Like previously mentioned, I’d guess the mint put it together (maybe to clear out some old stock by repackaging it in a new set). https://www.apmex.com/product/82361/1980-1986-great-britain-6-coin-gold-1-2-sovereign-proof-set
Thing is if and when the mint puts sets like that together and sells them, then those sets are listed someplace (in official reports) as having been sold by the mint. When there are no such reports then the mint didn't sell them - they are after market sets such as those I described. Now as I said to begin with, I'm not claiming that is definitely the case with this example, I have not done any checking. But apparently you guys have done some checking, and from what I can tell found nothing. Food for thought.