Coins that did not exist, coins that do not exist

Just asking, any of you know any extinct coins or coins that were not known to exist?
( http://www.ts.fi/uutiset/kotimaa/834854/Kuolinpesasta+loytyi+kolikko+jota+ei+pitaisi+olla+olemassa )
One of these coins was the 20MK 1957 copper coin. It could be added to numista, too! The story is interesting. The coin was minted either as a pattern or a error in 1957, tests have proven it. Something happened, it was forgotten until a person who owned it died.
In Finland as well as many other countries, when a person dies, the worth of his/her posessions is counted, and split into pieces...But someone found, a coin that should not exist. This meaning that there is no information on anything about this coin.

Most likely this coin was a natural error. The coin was found in 2015. Quite an interesting piece of history.

We have the 20 lei 1868 from Romania:
http://romaniancoins.org/20lei1868.html

Prince Carol I gave these coins as gifts to the Europe's crowned heads shortly subsequently to becoming the ruler of Romania, and also to his relatives and Romanian political chiefs. Of course, it is pointless to say that the coin did not circulate at all. Because it was never released for circulation, 20 lei 1868 coin is considered by many to be a pattern.

A hard to believe yet dear to the Romanian numismatics legend states that some of these coins were buried in the time capsule at the foundation of the Peleş castle at Sinaia. The coin was struck in 1868, and the castle built five years later in 1873, having been meant to resemble the Sigmaringen castle (the Romanian royal dinasty belonged to the Sigmaringen strain of the Hohenzollern family).

For modern Japan there are Y#151 and Y#152 both were never issued and remelted. Some of the designs were reused later.
But I don't know why they even got catalog numbers, maybe they were announced then abruptly recalled.

For UK coins ...
https://en.numista.com/forum/topic13824.html

1952 1 Penny [1949-1952 George VI]
https://en.numista.com/catalogue/pieces7604.html
"One 1952 penny, believed to be unique, was struck by the Royal Mint"

1952 2 Shillings 6 Pence [Half Crown] [1949-1952 George VI]
https://en.numista.com/catalogue/pieces1296.html
See http://www.colincooke.com/coin_images/halfcrowns/1952.html

1954 1 Penny [1954-1970 Elizabeth II]
https://en.numista.com/catalogue/pieces858.html
"At least one 1954 penny was struck, apparently for private internal purposes at the Royal Mint"

Quotes from Wikipedia.

Would the Great British coinage of "Edward VIII" be included, as he was obviously never crowned?

Here's one from a country I referee for, Hong Kong; it's interesting story was bought to my attention by a friend of mine who lives there, SquareRootLolly a few months ago:
https://en.numista.com/catalogue/pieces21708.html

https://www.ngccoin.com/news/article/4857/The-Intriguing-Tale-Of-The-1941-Hong-Kong-Cent/

"According to the World Coin Price Guide, the 5 million 1941 Hong Kong Cents were split into three lots. One was retained by Britain and ultimately melted to supply copper for the war effort. The second batch actually made it to Hong Kong, but it met the same fate of the first after the colony surrendered to Japan in December of 1941. In fact, Pridmore states that all coins available in the entire colony were collected and melted by the Japanese to help support their military. The third and final shipment ended up at the bottom of the ocean after the British ship it was on was sunk, likely by a German U-Boat. If any of these three groups of 1941 Hong Kong cents had survived, the coin would likely be relatively common today. However, the perfect combination of events has led this coin to become one of the most expensive and rarest dates of British Territory Hong Kong Cents."

I am not sure where to classify this one. The story goes that in 1974, a member of the US Congress dropped a penny next to a postal worker. The postal worker picks it up and tries to give the penny back to the Congressman. The Congressman tells the postal worker to keep the Penny. The penny turned out to be made of aluminum and samples were given to members of Congress in order to vote on whether or not to start making the pennies from aluminum as opposed to copper. The postal worker finally gave the penny back to the US mint in 2016.

https://www.reuters.com/article/us-california-penny-idUSKCN0WK05Q