In 2009 the Royal Mint accidentally made around 200,000 20 pence coins which had no date on either side. This is the first mistake where they forgot to put the date on it for over 300 years. When they were first discovered in January they were selling for as much as £400, however as more were beginning to be found the price began to fall. Now they usually sell for around £50 on Ebay because due to the large supply interest towards them fell with time. This price depends on the condition of the coin with those in better condition selling for more. When they were first found there were a lot of scams regarding the 20p coin as scammers were listing coins which were dateless only on one side, however these are the normal 20 pence coins which are only missing the date on the tail side of the coin. Although these scams are not illegal as they were advertising what they were selling, however a lot of buyers fell into this trap. Another scam included filing the date off the coin, but this led to a wide space on the bottom left side of the coin, whereas there was no obvious space on the mule coin. If you have found one of these coins the best thing to do would be to list it on Ebay and hope for the buyers to bid the price up, however remember that the coin has to have no date on either side to be the one that collectors are looking for.
